fs: handle recursive opendir bufferSize asynchronously

[mohin-io]

Summary

• use async dir handle reads when draining recursive queues so small bufferSize iterations don't block the event loop
• centralize buffered dirent emission to keep recursion logic consistent for sync, callback, and promise based reads
• add a regression test covering fs.promises.opendir with recursive reads and bufferSize: 1

Testing

• python tools/test.py sequential/test-fs-opendir-recursive (fails: missing built Release/node executable)

Fixes: #55764

[github-actions]

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