stream: inline unbuffered _write

PR-URL: https://github.com/nodejs/node/pull/32886


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>