Refactor cache validation and optimize alignment wizard incremental updates

- Extract cache mismatch logic into reusable cache_mismatch_reasons() function
  for cleaner validation and consistent miss reporting
- Expose memory_budget_bytes() for external callers (aligned exporter)
- Optimize rebuild_stack() with incremental layer updates when only one angle
  parameters change, avoiding full reprojection overhead
- Remove unused seed_per_angle parameter from alignment wizard
- Simplify cached_rf_image() DC masking with cleaner early exit logic
- Clean up internal state tracking with explicit origin caching

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

tests/test_gui.py

@@ -392,6 +392,14 @@ def test_wizard_nudges(ctx):
     assert len(wiz.state.layers) == s.n_angles, \
         "stack rebuilt for every angle after a rotation nudge"
 
+    # A nudge only reprojects the angle that moved, patching the overlap counts
+    # in place. That shortcut is only sound if it lands on exactly what a full
+    # rebuild would have produced.
+    incremental = wiz.state.counts.copy()
+    wiz.rebuild_stack()
+    assert np.array_equal(wiz.state.counts, incremental), \
+        "incremental nudge update matches a full stack rebuild"
+
     # Real key-event wiring (keyPressEvent -> signal -> slot).
     before = wiz.state.params[active].shift_mm
     QTest.keyClick(p1.canvas, Qt.Key.Key_Right)
@@ -529,7 +537,8 @@ def test_wizard_crop_dropped_when_going_back(ctx):
     pump(120)
     assert wiz.currentId() == wiz.PAGE_CORRELATE
     assert wiz.state.crop is None, "cleanupPage discarded the stale crop"
-    assert wiz.state.cropped_result is None
+    assert wiz.cropped_plan() == (None, None), \
+        "nothing derived from the dropped crop survives either"
     wiz.next()
     pump(150)
     assert wiz.state.crop is not None, "a fresh default crop is offered again"
@@ -546,8 +555,9 @@ def test_wizard_export(ctx):
         pump(150)
     assert wiz.currentId() == wiz.PAGE_SAVE, "advanced to the save page"
     ctx.p3 = p3 = wiz.page(wiz.PAGE_SAVE)
-    assert wiz.state.cropped_result is not None, "crop applied on leaving page 2"
-    assert wiz.state.cropped_result.canvas_shape == ctx.crop[2:], \
+    cropped, _ = wiz.cropped_plan()
+    assert cropped is not None, "crop applied on leaving page 2"
+    assert cropped.canvas_shape == ctx.crop[2:], \
         "cropped result carries the chosen shape"
     assert not p3.isComplete(), "Finish unavailable before anything is written"
     assert p3.lbl_summary.text(), "a summary of what will be written is shown"