basenc: ignore Interrupted errors

[andrewliebenow]

Mirror behavior of std::io::Read's read_to_end function (link): continue reading when errors with kind std::io::ErrorKind::Interrupted are encountered.

Also: clean up a few other things.

[github-actions[bot]]

GNU testsuite comparison:

GNU test failed: tests/timeout/timeout. tests/timeout/timeout is passing on 'main'. Maybe you have to rebase?

[github-actions[bot]]

GNU testsuite comparison:

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

[sylvestre]

Do you know if it is possible to test this?

[github-actions[bot]]

GNU testsuite comparison:

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