feat(ext/node): add fs.SyncWriteStream (#33226)
## Summary
Add `SyncWriteStream`, mirroring Node.js's
`lib/internal/fs/sync_write_stream.js`.
This is used for `process.stdout`/`process.stderr` when they are backed
by regular files (e.g. output redirected via `> file.txt`). It performs
synchronous writes via `fs.writeSync`, matching Node.js behavior for
FILE-type stdio descriptors.
Exported from `node:fs` as `fs.SyncWriteStream` (matching Node.js).
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
