fuzzing: add a new fuzzer for cksum

[sylvestre]

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/rm/rm2 is no longer failing!

[sylvestre]

Just a few early comments. Is there a way to easily inspect a handful of generated command-lines?

Just run :)

cargo +nightly fuzz run fuzz_cksum -- -max_total_time=60 -detect_leaks=0

[github-actions[bot]]

GNU testsuite comparison:

Skipping an intermittent issue tests/rm/rm1 (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)