Remove helper types

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.

src/mcp/server/models.py

@@ -0,0 +1,19 @@
+"""
+This module provides simpler types to use with the server for managing prompts
+and tools.
+"""
+
+from dataclasses import dataclass
+from typing import Literal
+
+from pydantic import BaseModel
+
+from mcp.types import (
+    ServerCapabilities,
+)
+
+
+class InitializationOptions(BaseModel):
+    server_name: str
+    server_version: str
+    capabilities: ServerCapabilities