[PATCH] fsck: add --workers option to configure worker threads

[Nithurshen]

As you know, currently decompression process in fsck.erofs is currently
strictly single threaded. In fsck/main.c, erofs_verify_inode_data
still processes blocks synchronously via a standard while loop.
Without wiring this flag to the workqueue engine in lib/workqueue.c,
the option doesn't currently change the tool's behavior.

And as you know "Multi-threaded Decompression Support in fsck.erofs"
is actually an official GSoC 2026 project idea and the project will
likely involve a comprehensive design of the parallelized
architecture, landing just the --workers CLI portion now might be
premature or conflict with the eventual design chosen by the GSoC
contributor.

I'd suggest reaching out to the mentors on the list to see if they
want to hold off on this patch until the GSoC project kicks off.
Also, if you do send a v2, switching to strtol() would be safer to
avoid potential -1 wrap-around issues on 32-bit systems.

Best,
Nithurshen