tr: fix "space" class, test "blank" class for order

[BenWiederhake]

This addresses a stand-alone issue originally documented in #6133, but can be solved independently: Our space class was wrong. As a drive-by, I also wrote a test to make sure our space class never gets messed up.

[BenWiederhake]

CI is flaky:

• Windows throws some errors similar to Windows CI is broken #6033, not sure if identical
• fuzz_echo fails during corpus upload:

2024-03-29T00:06:14.1473580Z [command]/usr/bin/tar --posix -cf cache.tzst --exclude cache.tzst -P -C /home/runner/work/coreutils/coreutils --files-from manifest.txt --use-compress-program zstdmt
2024-03-29T00:06:14.2280795Z Failed to save: Unable to reserve cache with key corpus-cache-fuzz_echo, another job may be creating this cache. More details: {"$id":"1","innerException":null,"message":"Request was blocked due to exceeding usage of resource 'Count' in namespace '.","typeName":"Microsoft.TeamFoundation.Framework.Server.RequestBlockedException, Microsoft.TeamFoundation.Framework.Server","typeKey":"RequestBlockedException","errorCode":0,"eventId":3000}`

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)

[cakebaker]

Thanks :)