http: fast-forward teardown of unread messages

[mcollina]

When a response finishes and the incoming message was fully received but never read (every body-less request that the handler ignores), _dump() currently calls resume(), which schedules a resume_ tick, emits 'resume' to no listeners, and runs the flow() machinery just to reach EOF.

With this change _dump() calls read(0) instead when the message is already ended, undestroyed and fully drained: read(0) at EOF goes straight to endReadable() (idempotent since #65310), so the 'end'/'close' sequence is unchanged and still asynchronous. Incomplete messages (body still arriving when the response ends) keep the resume() path. Unread client responses dumped by _http_client benefit the same way.

For a hello-world HTTP server this removes one nextTick (7 → 6 per request) and one dead emit (9 → 8 per request).

Benchmark (i7-7700, server pinned to one core, wrk -t2 -c50 on separate physical cores, 8 interleaved rounds; CPU measured from /proc/<pid>/stat over the run):

	CPU µs/request	user µs/request
main	26.6	16.7
this PR	25.3 (−4.2%)	15.8 (−5%)

The patched binary won all 8 rounds and served ~4% more requests per round.

test/parallel/test-http-*, test-stream-*, test-net-* and test-https-* all pass; test-http-dump-req-when-res-ends covers the mid-body dump case, which keeps the previous behavior.

——

This was generated with the assistance of AI. I reviewed all the code.

[nodejs-github-bot]

Review requested:

• @nodejs/http
• @nodejs/net

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.04%. Comparing base (7b0de5e) to head (803bd87).
⚠️ Report is 56 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65732      +/-   ##
==========================================
- Coverage   90.05%   90.04%   -0.01%     
==========================================
  Files         754      754              
  Lines      255722   256525     +803     
  Branches    48314    48530     +216     
==========================================
+ Hits       230281   230996     +715     
- Misses      16555    16645      +90     
+ Partials     8886     8884       -2     

Files with missing lines	Coverage Δ
lib/_http_incoming.js	97.96% <100.00%> (+0.02%)	⬆️

... and 70 files with indirect coverage changes

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