Move conformance tests to per-version directories

Conformance tests now live in conformance/<version>/*.py and are checked
against the corresponding stubs in dist/<version>/. Auto-detection only
runs versions that have both stubs and test files.

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

conformance/5.1/test_mathutils.py

@@ -0,0 +1,18 @@
+import mathutils
+from math import radians
+
+vec = mathutils.Vector((1.0, 2.0, 3.0))
+
+mat_rot = mathutils.Matrix.Rotation(radians(90.0), 4, "X")
+mat_trans = mathutils.Matrix.Translation(vec)
+
+mat = mat_trans @ mat_rot
+mat.invert()
+
+mat3 = mat.to_3x3()
+quat1 = mat.to_quaternion()
+quat2 = mat3.to_quaternion()
+
+quat_diff = quat1.rotation_difference(quat2)
+
+print(quat_diff.angle)