Update 5.1 conformance tests with memoryview and euler, improve conformance output

- Enable memoryview() tests in 5.1 conformance (Python 3.13 supports __buffer__)
- Add test_mathutils_euler.py for 5.1 conformance
- Show Python version in conformance check output

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

conformance/5.1/test_mathutils_quaternion.py

@@ -36,5 +36,5 @@ quat_avg = mathutils.Quaternion(exp_avg)
 print("Average rotation:")
 print(quat_avg)
 
-# Direct buffer access is supported at runtime via C buffer protocol
-# but not expressible in type stubs (requires Python 3.12+ __buffer__).
+# Direct buffer access is supported.
+print(memoryview(quat_avg).tobytes())