Replace per-plane pixel_scale/viewing_angle with z_tolerance; split pointing angle

MeasurementPlane now carries a z_tolerance (uniform tolerance mechanism)
instead of the removed pixel_scale/viewing_angle_deg fields.
ReconstructionResult.pointing_angle_deg becomes horizontal/vertical fields
to match the beam's two independent tilt degrees of freedom.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_plotting.py

@@ -11,7 +11,8 @@ def make_result(**overrides):
         purity={(0, 0): (0.9, 0.1), (1, 0): (0.1, -0.2)},
         reconstructed_field=np.zeros((5, 5), dtype=complex),
         centers=[(0.0, 0.0), (1e-4, -1e-4), (2e-4, -2e-4)],
-        pointing_angle_deg=0.5,
+        pointing_angle_horizontal_deg=0.3,
+        pointing_angle_vertical_deg=0.4,
         residuals=[np.ones((5, 5)), np.ones((5, 5)) * 2, np.ones((5, 5)) * 3],
     )
     defaults.update(overrides)