`ESRCH` is not handled by file io operations

[breavyn]

Zig Version

0.12.0

Steps to Reproduce and Observed Behavior

Reading or writing files under /proc/<pid>/ on linux can result in an ESRCH error if the related process has terminated.

Functions read, pread, readv, etc. and their write counterparts, seek, and possibly others, return error.Unexpected in this case.

Expected Behavior

Functions should return error.ProcessNotFound on ESRCH.