Resolve pandas deprecations

[finozzifa]

Closes # (if applicable).

Closes issue #314

Changes proposed in this Pull Request

Resolve the pandas deprecations listed in issue #314.

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Newly introduced dependencies are added to envs/environment.yaml and envs/environment.docs.yaml.
• Changes in configuration options are added in all of config.default.yaml, config.tutorial.yaml, and test/config.test1.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[davide-f]

Great @finozzifa :D
To me the code seems smooth, really great job and pace!
I see the use of .T that sometimes can be a bit tricky; have you tested and verified that outputs numerically match?
By reviewing the code, it seems fine, but I'd personally perform two checks:

1. that in debug the output of that code works fine
2. the output of the solve_network is the same as before
   I'm sure you have done that, this is maybe being extra cautious, apologies