Your solutions are very broken.
All of your solutions require the last non-space character to be an uppercase letter. You could say you're investigating a subset of the original question, except that your input has no uppercase letters. Use \s or a space instead of [^A-Z]. Use \S instead of [A-Z].
Some of your solutions have problems with trailing newlines due to the missing "s" modifier. /./ doesn't match newlines without it.
All but the last of your solutions don't work if the input is made entirely of spaces.
There's also a issue with your benchmark. Benchmarking code that removes trailing spaces when your input never has trailing spaces is odd. Include a case where the input has trailing spaces!