Factor the connection-backed write handle pool out of the smb backend into a generic lib/filepool.Pool[T] with its own tests, so it can be reused by other backends that implement fs.OpenWriterAter over a connection pool. The smb backend keeps its behaviour, opening and releasing handles through small closures passed to the pool. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Signed-off-by: Splainte <r.wycke@hotmail.fr>