Restore the Buffer.isBuffer() check to avoid unnecessary Buffer.from()
calls when the input is already a Buffer. This improves performance
by 30-50% for buffer-heavy UDP operations.
Includes benchmark test for fixBufferList function to verify the
performance improvements across different data types and chunk sizes.
PR-URL: https://github.com/nodejs/node/pull/59934
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>