Decode Transfer-Encoding: gzip response bodies incrementally

[oalders]

Summary

Net::HTTP::Methods::read_entity_body handled a Transfer-Encoding: gzip
response body by accumulating every de-chunked byte in a closure-local buffer
and gunzipping the whole thing in a single pass once the terminating
zero-length chunk arrived, then returning a scalar reference to the result.

That has two problems:

1. The read cap is never consulted while the body streams. Each read
   returned "" (surfaced upstream as -1, "read again"), so the buffer grew
   with no upper bound until the stream ended. A caller's read/size cap — e.g.
   LWP::UserAgent's max_size, enforced in LWP::Protocol::collect — only
   sees the body after it has already been fully buffered and decompressed,
   which defeats the point of the cap. Compression ratios stack on top of this.

2. Size accounting is wrong. Because the closure returned a reference,
   length() measured the stringified reference (~19 bytes) rather than the
   decoded payload.

Fix

Decode incrementally with Compress::Raw::Zlib::Inflate->new(WindowBits => WANT_GZIP),
mirroring the deflate branch immediately above it. Each read now returns a
plain string of just-decoded bytes, so:

• length() is truthful,
• a caller's read cap applies on every read, and
• peak memory tracks the read size instead of the whole response size.

Tests

• New t/te-gzip.t builds a gzip, chunked response split across many small
  chunks and asserts correct decoding, truthful per-read lengths, and
  incremental delivery. It fails against the previous code (returns a
  SCALAR(0x…)) and passes with this change.
• Existing t/http.t and t/socket-class.t continue to pass.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 68.09%. Comparing base (dc1a5d2) to head (3cd7927).

Files with missing lines	Patch %	Lines
lib/Net/HTTP/Methods.pm	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #96      +/-   ##
==========================================
+ Coverage   62.43%   68.09%   +5.65%     
==========================================
  Files           4        4              
  Lines         402      398       -4     
  Branches      108      107       -1     
==========================================
+ Hits          251      271      +20     
+ Misses        104       80      -24     
  Partials       47       47              

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