refactor!: remove waterworld env and tests

[virgilt]

Description

This PR removes the Waterworld environment from PettingZoo.
The environment has been unmaintained for multiple versions and has caused ongoing CI failures due to outdated imports and tests.

This change fully removes:

• All pettingzoo/sisl/waterworld source files
• All corresponding tests and documentation references
• Any residual CI or import references related to Waterworld

Type of change

Please delete options that are not relevant.

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Screenshots

Not applicable (codebase cleanup, no visual changes).

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have run pytest -v and no errors are present.
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I solved any possible warnings that pytest -v has generated that are related to my code to the best of my knowledge.
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes