chore(deps): fastmcp 4 (mcp 2.2)

No code change needed: the server side (`FastMCP`, `@mcp.tool`,
`get_http_headers`, `http_app`) and the client side (`Client`, `BearerAuth`,
the three transports, and the `mcp.client.auth` / `mcp.shared.auth` OAuth
types imported directly) all kept their signatures.

Verified beyond the suite by driving the real `/mcp` mount over a live
uvicorn socket with the fastmcp client: tool discovery, a `search_docs` call
and bearer-token extraction all round-trip, with the token reaching
`search()` intact.

fastmcp 4 and mcp 2.2 also moved to httpx2, so the retry tuple's comment now
places them on that side of the split.

tests/llm/test_fallback.py

@@ -372,9 +372,10 @@ class TestStreamingFallback:
         self, patch_model_utils, error
     ):
         """The providers are split across two HTTP stacks whose exception
-        classes are unrelated types: openai and anthropic raise from httpx2,
-        google-genai and elevenlabs still from httpx. Naming one stack makes
-        the retry silently stop firing for the other half.
+        classes are unrelated types: openai, anthropic and the MCP client
+        raise from httpx2, google-genai and elevenlabs still from httpx.
+        Naming one stack makes the retry silently stop firing for the other
+        half.
         """
         backup = FakeLLM(stream_chunks=["fallback"])
         patch_model_utils(