fix(h1): complete paused parser on socket end instead of crashing

[ronag]

When a response body applies backpressure, the HTTP/1 llhttp parser is
left paused. If the peer then closes the socket, onHttpSocketEnd calls
parser.finish(), which asserted !this.paused and crashed the process
with an uncatchable AssertionError from the socket 'end' handler.

finish() now resumes a paused parser and drains the socket through it so
the response completes correctly across all body framings:

• Content-Length / chunked bodies reach on_message_complete during
  execute() (driving the parser past the body is required; calling
  llhttp_finish() alone leaves them hanging).
• EOF-delimited bodies (no length) can't complete via execute() and
  re-pause, so we resume once more and let llhttp_finish() deliver the
  EOF completion.
• Backpressure is advisory here (onData keeps buffering delivered bytes),
  so we resume across pauses and loop until the socket buffer is empty,
  rather than parsing only a single read().

Truncated responses still surface as errors, never a false completion:
short Content-Length -> UND_ERR_RES_CONTENT_LENGTH_MISMATCH, unterminated
chunked -> HTTPParserError.

Fixes #5360. Supersedes #5364, whose fix hangs
Content-Length bodies (resume without execute) and whose test passes
without the fix (the 'data' listener switches the stream to flowing mode
so the parser never pauses). The tests here keep the body unconsumed
until after FIN and cover Content-Length/EOF completion plus
Content-Length/chunked truncation; all four fail against the unpatched
parser.

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.45%. Comparing base (ce7bf4f) to head (c52fa90).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5474      +/-   ##
==========================================
- Coverage   93.46%   93.45%   -0.01%     
==========================================
  Files         110      110              
  Lines       37124    37147      +23     
==========================================
+ Hits        34698    34717      +19     
- Misses       2426     2430       +4     

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[mcollina]

lgtm