The helper types in mcp.server.types got really confusioning during
implementation as they overlapped with mcp.types. I now believe it
is better if we stay more low level to the spec types.
To do this, we now only use mcp.types everywhere. We renamed mcp.server.types
to mcp.server.models and removed it to the absolute minimum.
Replace generic capability dictionaries with structured types for prompts,
resources, tools, and roots. This improves type safety and makes capability
features like listChanged and subscribe more explicit in the protocol.
