2026-03-07 Stabilize experimental python SDK foundation

Description:
- pin datamodel-code-generator to an exact version and invoke it through the active interpreter
- make generate_types own the maintained generated surfaces and regenerate committed artifacts
- make sdk/python tests hermetic and regeneration checks idempotent

sdk/python/tests/conftest.py

@@ -0,0 +1,10 @@
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+SRC = ROOT / "src"
+
+if str(SRC) not in sys.path:
+    sys.path.insert(0, str(SRC))