cksum: fix parsing error with tagged cheksum files

[frenchua]

When passed the '-c'/'--check' flag, and parsing a checksum file in the "tagged" format, cksum (symlinked to sha256sum, etc...) expects a line that looks like this:

ShA256 (file.bin) = da39a3ee5e6b4b0d3255bfef95601890afd80709

If the hash algorithm at the beginning of the line (in the above case SHA256) is missing, then cksum panics because it is attempts to use the value of an array at index -1. This fix causes cksum to instead consider the line a syntax error and ignore it, just as GNU cksum does. I also added unit and integration tests to check for the above behaviour.

(This is a second PR I made concerning this issue. I closed the previous one becuase I can't figure out how git rebase can be used to squash non-contiguous commits, but I think I've learned how to use it now).

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/io-errors. tests/misc/io-errors is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/io-errors. tests/misc/io-errors is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/cut/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/expand/bounded-memory is now passing!

[frenchua]

Concerning the one failed check:

Both test_create_one_fifo_with_non_file_permission_mode and test_create_one_fifo_already_exists pass on my local machine (Intel Macbook), both on my branch and main. I'll try again on ubuntu. But I don't see how any changes I made could possibly affect the outcomes of these tests.