fs: add Blob support to writeFile and appendFile

[aelhor]

This PR addresses part of #61684 by adding Blob support to the writeFile / appendFile family:

• fsPromises.writeFile(data)
• fsPromises.appendFile(data) (also broadens the documented data union from {string|Buffer} to the full set)
• filehandle.writeFile(data)
• filehandle.appendFile(data)

Implementation

A Blob is converted to a web ReadableStream via blob.stream() and consumed through the existing async-iterable path in writeFile. This is a small, ~6-line change that reuses existing infrastructure. Native zero-copy via a C++ blob handle is explicitly deferred as future work.

Tests

New test/parallel/test-fs-writefile-blob.js covers all 4 entry points, plus empty blob, binary blob, large blob (multi-chunk), explicit encoding option, and AbortSignal cancellation.

Scope: this covers the writeFile/appendFile portion of the issue's first ask. Remaining items from #61684 (the positional filehandle.write(blob), and the web fs.createWritableStream counterpart) will be tracked as separate follow-up PRs to keep this focused.

Refs: #61684

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.13%. Comparing base (00917ba) to head (e8258fd).
⚠️ Report is 1347 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64611      +/-   ##
==========================================
- Coverage   90.14%   90.13%   -0.02%     
==========================================
  Files         741      741              
  Lines      242076   242081       +5     
  Branches    45558    45553       -5     
==========================================
- Hits       218216   218190      -26     
- Misses      15385    15401      +16     
- Partials     8475     8490      +15     

Files with missing lines	Coverage Δ
lib/internal/fs/promises.js	93.01% <100.00%> (+0.01%)	⬆️

... and 31 files with indirect coverage changes

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[aelhor]

Could someone from the fs team take another look at this? The previous approval became stale after the latest changes, and the PR now just needs one reapproval to unblock the merge. Thanks!

[aelhor]

@jasnell Friendly ping when you have a moment. I corrected only the commit message; the code itself is unchanged, but this made the previous approval stale. Could you please review and re-approve the latest commit? Thank you!

[aelhor]

the issue actually asks. Use this corrected body instead:

Does this text belong in the PR text? It looks like it was an agent-generated instructions.

You are right, I updated the pr body

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78106/

[MikeMcC399]

Jenkins CI is showing successful, so I've marked the PR as author ready PRs with CI started, the required approvals, and no outstanding review comments.

[aelhor]

Jenkins CI is showing successful, so I've marked the PR as author ready PRs with CI started, the required approvals, and no outstanding review comments.

Thanks @MikeMcC399 for running the CI and updating the status!