fs: add Blob support to writeFile and appendFile

[aelhor]

the issue actually asks. Use this corrected body instead:
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 3 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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