Fix docs rendering for classes using lazy import

[Lilly-May]

Issue

The lazy_import introduced in PR #647 solves the issue of a failed pertpy import when not all optional dependencies are installed. However, since the classes were wrapped in multiple functions, they were no longer correctly displayed in the docs.

Description of changes

• Updated the implementation of the lazy_import method: Instead of wrapping the class in a function, I created a Placeholder class that raises an ImportError when called. This should be equivalent to the previous implementation functionality-wise. I verified that one can import pertpy when optional dependencies are not installed in the environment, and that the docs builds correctly as long as the optional dependencies are installed.
• Removed python version descriptions from the Apple Silicon installation guide, as including them would only cause the guide to be outdated
• Fixed SCGEN display in docs/usage.md (updated method name)
• Removed edger from the required packages in tools/__init__. EdgeR is installed/imported via rpy2, so checking that edger can be directly imported will fail, making the EdgeR implementation in pertpy unusable.
• With the new anndata 0.10.9 release, anndata only allows numpy.matrix classes to be stored in varm/obsm (see 3rd bullet point of release notes here). This caused the cinemaot and PyDeseq2 tests to fail. I resolved the former by storing a numpy array instead of a JAX array in the anndata. The latter issue is due to a bug in the pydeseq package itself, so I can't resolve that one, but I have opened an issue here.

[Zethson]

Thank you very much!