Closes #5231

I could not get the lazy imports feature to actually fully work with our library, somewhere along the path all dependencies are eagerly resolved. Doing lazy import telegram does work and everything is lazy, until you first use just one class, and then everything is imported all at once, which defeats the point. I may look more deeply into this later.

• There are other some non-critical warnings which show up, related to sphinx, but so far I've not noticed that breaking anything. Tracking issue: PEP 829: KeyError: "local variable ''sitedir'' is not defined" python/cpython#149671

• This PR also bumps the cryptography version, which allows it to build on 3.15.

• Free threaded build fails on 3.15 due to cryptography fails to build on 3.15t with uv pyca/cryptography#14983. For now we should say that we don't fully support 3.15t.