[WIP] remove inplace for pandas cat

[Japhiolite]

Description

inplace=True has been deprecated completely with Pandas 2.0. I think Alex started changing this in the past, but the changes (or I misremember) are not present in this branch.

Checklist

• My code follows the PEP 8 style guidelines.
• My code uses type hinting for function and method arguments and return values.
• My code contains descriptive and helpful docstrings
  which are formatted per the Google Python Style Guidelines.
• [ x ] I have created tests which entirely cover my code.
• [ x ] The test code either 1. demonstrates at least one valuable use case (e.g. integration tests)
  or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
• [ x ] New and existing tests pass locally with my changes.

[Japhiolite]

ok, pip tests are now passing...but some unit tests will fail again with pandas 2.0.2 (now testing environment is 2.0.1)...
haven't looked into this yet