chore(clippy): the lints newer toolchains enforce

[bdelanghe]

rust-toolchain.toml pins 1.94.0 and CI installs exactly that, so nothing in this repo has ever been checked against a newer clippy. Anyone whose toolchain comes from somewhere else — nixpkgs currently ships 1.97 — gets eight errors on a clean tree, which makes just clippy useless to them.

Found while wiring up #250 (a devShell), where gate_clippy was the one gate that would not go green.

All mechanical, no behaviour change

lint	sites	change
unnecessary_sort_by	6	flipped comparator → sort_by_key with std::cmp::Reverse
needless_borrows_for_generic_args	2	drop a & in a println! argument that Display takes by reference anyway

crates/path-cli/src/cache.rs:135
crates/path-cli/src/cmd_import.rs:593,785
crates/path-cli/src/cmd_list.rs:378,398,550,571
crates/path-cli/src/sync/engine.rs:152
crates/toolpath-pi/src/reader.rs:359

Every sort keeps its ordering — all six were "newest first", and Reverse on a Copy key (SystemTime, Option<DateTime<Utc>>) expresses that directly rather than leaving the reader to work out which side of the comparison was swapped.

The 1.94.0 pin is untouched. This does not adopt a newer toolchain; it only removes the gap between the pinned one and later releases, so the tree is clean under both.

Verified under 1.97

cargo clippy --workspace -- -D warnings     clean
cargo fmt --all --check                     clean
cargo test -p path-cli --lib                418 passed, 0 failed
cargo test -p toolpath-pi --lib             133 passed, 0 failed

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1. Independent PR — no bundled or speculative changes
   • Verified: one concern — lints that newer clippy enforces. No behaviour change, no new lint allows, no toolchain bump.
2. Changed codepaths verified — targeted unit and full integration tests
   • Verified: path-cli 418 and toolpath-pi 133 unit tests pass; clippy and fmt clean under 1.97
3. Root cause identified — every failure traced to source
   • The pin means CI only ever exercises 1.94.0; unnecessary_sort_by and needless_borrows_for_generic_args tightened in later releases, so the gap only shows on a toolchain from elsewhere
4. No duplication — refactoring preferred over copy/paste
   • Same rewrite applied uniformly at all six sort sites rather than special-casing any
5. No unrelated changes — housekeeping isolated to its own branch
   • This is the housekeeping branch; the devShell (build(nix): a devshell, so the justfile's cargo is really there #250) and the test-sandbox fix (test(cli): the sandbox holds when CLAUDE_CONFIG_DIR is set #251) are separate

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