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_vector.py

@@ -54,5 +54,5 @@ vec.xy = vec4d.zw
 vec.xyz = vec4d.wzz
 vec4d.wxyz = vec.yxyx
 
-# 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.
+raw_data = memoryview(vec).tobytes()