Pandas 2.0 compatibility

[gtca]

This PR improves compatibility with Pandas 2.0.

For a start, this PR will

• Fix #39
• Address #40

[codecov-commenter]

Codecov Report

Merging #43 (c567cb0) into master (baac912) will increase coverage by 0.12%. The diff coverage is 86.66%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #43 +/- ## ========================================== + Coverage 69.25% 69.38% +0.12% ========================================== Files 14 14 Lines 1633 1653 +20 ========================================== + Hits 1131 1147 +16 - Misses 502 506 +4 ``` | [Impacted Files](https://app.codecov.io/gh/scverse/mudata/pull/43?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse) | Coverage Δ | | |---|---|---| | [mudata/\_core/utils.py](https://app.codecov.io/gh/scverse/mudata/pull/43?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse#diff-bXVkYXRhL19jb3JlL3V0aWxzLnB5) | `85.71% <63.63%> (-14.29%)` | :arrow_down: | | [mudata/\_core/mudata.py](https://app.codecov.io/gh/scverse/mudata/pull/43?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse#diff-bXVkYXRhL19jb3JlL211ZGF0YS5weQ==) | `63.18% <100.00%> (ø)` | | | [tests/test\_view\_copy.py](https://app.codecov.io/gh/scverse/mudata/pull/43?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse#diff-dGVzdHMvdGVzdF92aWV3X2NvcHkucHk=) | `100.00% <100.00%> (ø)` | |