#[fs_init]Expand description
Sibling to [dtact_io_init] for the fs module: configures and starts
whichever native fs backend is active (io_uring slot pool on Linux,
IOCP slot pool on Windows, thread pool elsewhere — see
dtact_util::fs::init_fs) before the wrapped main/entry point runs.
Takes the same five knobs as dtact_io_init (workers,
buffer_pool_size, chunk_size, pin_cpus, ring_depth); ring_depth
is what actually sizes the preallocated op-slot pool for fs ops.