stream: prevent enqueue after cancel in Readable.toWeb()

[kairosci]

This pull request resolves an issue where converting a Node readable stream to a web stream using the toWeb method could result in an uncatchable exception when the stream is cancelled during a backpressure resume cycle. When the cancel method is invoked on the underlying source, the controller transitions to a closed state but the data listener remains attached to the source stream. Consequently, a scheduled flow tick may deliver an additional data event which triggers an invalid state error upon attempting to enqueue the chunk into the already closed controller. To fix this behavior structurally, a cancellation guard is added directly inside the data event listener to intercept and discard any incoming chunks once the stream has been marked as cancelled. A regression test is also included to ensure that disconnecting a pipeline under backpressure properly tears down the stream without throwing uncaught exceptions.

Fixes: #64529

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/75179/

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.16%. Comparing base (54a5095) to head (3710995).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/adapters.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64766      +/-   ##
==========================================
+ Coverage   90.14%   90.16%   +0.01%     
==========================================
  Files         744      744              
  Lines      242518   242519       +1     
  Branches    45685    45691       +6     
==========================================
+ Hits       218611   218660      +49     
+ Misses      15396    15361      -35     
+ Partials     8511     8498      -13     

Files with missing lines	Coverage Δ
lib/internal/webstreams/adapters.js	86.62% <0.00%> (-0.08%)	⬇️

... and 37 files with indirect coverage changes

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[kairosci]

Sorry, missclicked.

Anyway, there were a few linting issues in test/parallel/test-webstreams-adapters-cancel-backpressure.js.

I removed some trailing spaces on empty lines.

I wrapped the .then() callbacks and the test exit in common.mustCall() to satisfy the node-core/must-call-assert ESLint rule, which requires Node's test runner to track promise settlements explicitly.

I properly declared const common = require('../common'); instead of just requiring it.

Commit message used webstreams:, but the correct subsystem prefix for this file is stream:.

I amended commit message from webstreams: prevent enqueue after cancel in Readable.toWeb() to stream: prevent enqueue after cancel in Readable.toWeb().