CLN: remove unneeded inheritance from base object
- [x] xref #25725

Bit of a tedious whopper to review (sorry), but this PR removes all instances of inheriting from the base ``object`` from the code base, as dropping Python2 support means that this particular idiom is no longer needed. 

Additionally, as part of the above, I've removed the check in code_checks.sh that classes must inherit, as that is no longer a requirement after dropping Python2. I don't think a different check is possible to do now, but I can change instead of delete the check if anyone thinks that would make sense.
