fs: preserve readFile() errors for numeric file descriptors

[jibin7jose]

Summary

fs.readFile() with a numeric file descriptor and the new buffer option could lose errors on the user-fd path.

Root cause

In lib/internal/fs/read/context.js, ReadFileContext.close(err) did not forward err when isUserFd was true. As a result, failures that should have reached the callback, including an undersized caller-provided buffer, could be treated as successful completion.

Fix

Forward the close error for user-supplied file descriptors so the final callback receives the actual failure instead of silently succeeding.

Tests

Add regression coverage for the numeric file descriptor path with:

• a preallocated buffer
• a function-returned buffer
• a buffer that is too small

This verifies the error is preserved for the callback-based API.

Fixes: #64367

[jibin7jose]

Hi @joyeecheung, could you please take a look at this PR when you have a chance? It fixes an issue where fs.readFile() with a numeric file descriptor and the new buffer option could lose errors on the user-FD path. I've added regression tests covering the affected scenarios. Any feedback would be greatly appreciated. Thank you!

[joyeecheung]

I am not very familiar with this code any more, but it seems straightforward enough and from a glance it makes sense to me. Would be better if @addaleax can take a look since it was introduced in #35487

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/74917/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.23%. Comparing base (1912893) to head (8b57081).
⚠️ Report is 97 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #64368 +/- ##
==========================================
- Coverage 90.25% 90.23% -0.03% 
==========================================
Files 741 741 Lines 241165 241207 +42 Branches 45423 45426 +3 ==========================================
- Hits 217673 217655 -18 - Misses 15069 15120 +51 - Partials 8423 8432 +9 

Files with missing lines	Coverage Δ
lib/internal/fs/read/context.js	94.92% <100.00%> (ø)

... and 46 files with indirect coverage changes

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