Python SDK v2

[Kludex]

I'll use this issue to add notes about what I think should happen for V2.

• Use snake case instead of camel case on types.py (mcp.types.Tool is not following python's naming convention  #97)
• Don't use RootModel on types.py - It makes hard to reason about types.
• Revisit generic classes, and add more default values for them Excessive use of generics #1207
• Rethink ClientSessionGroup. It doesn't have a user-friendly API.
• Rename FastMCP to MCP (or suggestions welcome...)
• Add conveniences for MCP proxy pattern #12

I'll lock the issue, so only maintainers can comment, and I can focus on the things that I really think should be here.