test(fetch_tools): rewrite tests to use real MCP mock server

Replace monkeypatch-based tests with integration tests using the
actual MCP protocol via the Hono mock server. This provides more
realistic coverage of the fetch_tools() implementation.

Changes:
- Rename test_toolset_mcp.py to test_fetch_tools.py for clarity
- Use mcp_mock_server fixture for most tests (real MCP protocol)
- Keep monkeypatch tests only for schema normalisation logic
- Add integration marker for MCP server tests
- Add tests for MCP headers, tool creation, and RPC execution

The tests now exercise the full MCP client flow including
_fetch_mcp_tools(), header building, and tool response parsing.

Author: ryoppippi

pyproject.toml

@@ -69,6 +69,7 @@ asyncio_mode = "strict"
 asyncio_default_fixture_loop_scope = "function"
 markers = [
     "asyncio: mark test as async",
+    "integration: mark test as integration test requiring MCP mock server",
 ]
 
 [tool.ruff.lint.per-file-ignores]