gh-71679: Improve tests for repr() of bytes and bytearray (GH-138180)

* Merge existing tests test_repr_str and test_to_str.
* Add more tests for non-printable and non-ASCII bytes.
* Add tests for special escape sequences ('\t\n\r').
* Add tests for slashes.
* Add more tests for quotes.
* Add tests for subclasses.
* Add test for non-ASCII class name.
* Only apply @check_bytes_warnings for str() tests.