fix(fetch): dump 3xx redirect bodies without pausing so the connection is released

[pacocartones]

Fixes #5728.

Problem

fetch({ redirect: 'follow' }) hangs when a 3xx redirect body is large, on a connection-limited Agent. In httpNetworkFetch (lib/web/fetch/index.js), onResponseData pushed each chunk into the internal Readable and called controller.pause() on backpressure. A redirect body larger than the highWaterMark (the repro uses 128 KiB) fills the buffer, pauses the socket, and — since the follow path discards the response and recurses into mainFetch — the body is never consumed. The connection stays running; with Agent({ connections: 1 }) the follow-up can never acquire the pinned socket → hang.

The request() path (lib/handler/redirect-handler.js) already discards 3xx bodies without pausing, so it never pins the connection; the fetch path lacked the equivalent.

Fix

Set this.willFollow in onResponseStart, and in onResponseData return early when fetchParams.controller.dump || this.willFollow — discarding the bytes but not pausing, so the socket drains, onResponseEnd fires, and the connection is released. Per-hop (the handler is per-dispatch), and correct because a followed 3xx body is never exposed to the caller.

Test

test/issue-5728.js: RED timed out at 15s (hang); GREEN passes in ~31ms. Full redirect regression suite green (redirect-request 83, redirect-stream 23, fetch/redirect, client-fetch 33, …), npm run lint — all green.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.50%. Comparing base (17117f6) to head (e4ac1c2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5767   +/-   ##
=======================================
  Coverage   93.50%   93.50%           
=======================================
  Files         110      110           
  Lines       39072    39084   +12     
=======================================
+ Hits        36534    36547   +13     
+ Misses       2538     2537    -1     

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