Refactor async_context_manager type annotations using ParamSpec

[junyilou]

Refactored the type annotations for the async_context_manager decorator in asyncssh/misc.py by replacing Callable[..., ...] with ParamSpec (_ACMParam). By capturing parameter types with ParamSpec, static analysis tools and IDEs now accurately inspect and auto-complete the original function's arguments (names, types, and defaults) when calling decorated functions, significantly improving type safety and developer experience.

typing.ParamSpec was introduced in Python 3.10, which aligns with the project's target Python version.

[ronf]

Thanks for this PR! I experimented with ParamSpec early on, but never could get it working the way I wanted to. Also, as you pointed out, ParamSpec is now a part of Python 3.10 which is the minimum supported version by AsyncSSH, so this is a good time to revisit this.

Unfortunately, I'm still seeing errors from mypy after making this change:

asyncssh/sftp.py:4227: error: Argument 1 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4227: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4227: note:     Expected:
asyncssh/sftp.py:4227: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4227: note:     Got:
asyncssh/sftp.py:4227: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4338: error: Argument 2 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4338: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4338: note:     Expected:
asyncssh/sftp.py:4338: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4338: note:     Got:
asyncssh/sftp.py:4338: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4453: error: Argument 1 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4453: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4453: note:     Expected:
asyncssh/sftp.py:4453: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4453: note:     Got:
asyncssh/sftp.py:4453: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4453: error: Argument 2 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4453: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4453: note:     Expected:
asyncssh/sftp.py:4453: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4453: note:     Got:
asyncssh/sftp.py:4453: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4476: error: Argument 1 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4476: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4476: note:     Expected:
asyncssh/sftp.py:4476: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4476: note:     Got:
asyncssh/sftp.py:4476: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4499: error: Argument 2 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4499: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4499: note:     Expected:
asyncssh/sftp.py:4499: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4499: note:     Got:
asyncssh/sftp.py:4499: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4523: error: Argument 1 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4523: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4523: note:     Expected:
asyncssh/sftp.py:4523: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4523: note:     Got:
asyncssh/sftp.py:4523: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/sftp.py:4523: error: Argument 2 to "_begin_copy" of "SFTPClient" has incompatible type "SFTPClient"; expected "_SFTPFSProtocol"  [arg-type]
asyncssh/sftp.py:4523: note: Following member(s) of "SFTPClient" have conflicts:
asyncssh/sftp.py:4523: note:     Expected:
asyncssh/sftp.py:4523: note:         def open(path: bytes, mode: str, block_size: int = ...) -> _ACMWrapper[SFTPFileProtocol]
asyncssh/sftp.py:4523: note:     Got:
asyncssh/sftp.py:4523: note:         def open(path: bytes | str | PurePath, pflags_or_mode: int | str = ..., attrs: SFTPAttrs = ..., encoding: str | None = ..., errors: str = ..., block_size: int = ..., max_requests: int = ...) -> _ACMWrapper[SFTPClientFile]
asyncssh/connection.py:5201: error: Argument "tunnel" to "listen_reverse" has incompatible type "SSHClientConnection"; expected "tuple[()] | str | _TunnelListenerProtocol | None"  [arg-type]
asyncssh/connection.py:5599: error: Argument 1 to "create_server" of "SSHClientConnection" has incompatible type "Callable[[str, int], Awaitable[SSHUNIXSession[Any]]]"; expected "Callable[[str, int], SSHTCPSession[str] | Awaitable[SSHTCPSession[str]]]"  [arg-type]
asyncssh/connection.py:5640: error: Argument 1 to "create_unix_server" of "SSHClientConnection" has incompatible type "Callable[[], Awaitable[SSHTCPSession[bytes]]]"; expected "Callable[[], SSHUNIXSession[str] | Awaitable[SSHUNIXSession[str]]]"  [arg-type]
Generated HTML report (via XSLT): /tmp/cov/index.html
Found 11 errors in 2 files (checked 67 source files)

I still need to go through these errors in detail -- it's possible some of the Protocol classes need to be adjusted now that we're doing stricter type checking on these ACM types. If you see a way to address these, please let me know!