Resolve Pandas 2.2 (FutureWarning) issues

[martinvonk]

Short Description

This PR solves many of the future warning for Pandas 2.2 in advance to 3.0.

Related to issue #629

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Coverage summary from Codacy

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Coverage variation	Diff coverage
✅ +0.17% (target: +0.00%)	✅ 96.08%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (5251c97)	5991	4468	74.58%
Head commit (1071845)	5999 (+8)	4484 (+16)	74.75% (+0.17%)

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Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#684)	51	49	96.08%

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[martinvonk]

You want to merge this @raoulcollenteur before #686? I was not able to fix the FutureWarnings yet. That takes more time. But I did fix the failing test with Pandas. But if we merge this now, we can support more pandas versions in Pastas v1.4..

[martinvonk]

I added all FutureWarnings I found to #72. I have a feeling most things will be deprecated for Pandas 3.0 so we could add Pandas < 3.0 in the dependencies list.

[martinvonk]

Pandas 3.0 milestone is set for 1st of April: https://github.com/pandas-dev/pandas/milestone/102

[raoulcollenteur]

@martinvonk perhaps you can have a quick look at this?

I also opened a new issue for Pandas 3.0 #687 to track changes necessary that only work with pandas > 2.1.