Feature: speed up the mask painter

[yulewu]

The Mask Painter plugin is a powerful tool for visualizing and editing cell masks, but it significantly slow down the viewer when enabled, especially with large datasets.

Please look into why it is slow and optimize the performance.

[yulewu]

Update Summary: Mask Painter performance optimization (commit 8cd0f98)

Root cause: every render event (pan, zoom, FOV change, map-mode tile update) called four separate get_effective_*_map_for_fov methods on the painter, each independently invoking build_painter_state_maps_for_fov which filters the full cell table by FOV and iterates every matching row in Python. This meant O(N) work repeated 4× per render frame with no caching.

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Actions Taken

• Added get_effective_state_maps_for_fov(fov) to MaskPainterDisplay:
  Single method that calls build_painter_state_maps_for_fov once and returns all four maps. Results are cached per FOV in _state_maps_cache; cache is cleared in apply_colors_to_masks on any UI state change so pan/zoom with unchanged state is O(1).
• Updated _compose_fov_image in main_viewer.py:
  Replaced four separate painter map calls with one get_effective_state_maps_for_fov call.
• Updated _apply_map_painter_overlay in main_viewer.py:
  Consolidated the four per-FOV painter calls at the top of the tile loop into a single combined call, eliminating 4N cell-table passes for an N-FOV map render.
• Fixed pre-existing test failure:
  Corrected global_fill_opacity_input layout width from 150px to 95px to match the existing test assertion.
• Extended tests/bootstrap.py:
  Added stubs for BoundedIntText, select_dtypes, iterrows, element-wise Series operators, dtype, matplotlib.font_manager, and tifffile to enable mask painter tests in headless environments.

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Files Changed

• ueler/viewer/plugin/mask_painter.py — Added get_effective_state_maps_for_fov, _invalidate_state_maps_cache, _state_maps_cache; fixed opacity input width; invalidation in apply_colors_to_masks
• ueler/viewer/main_viewer.py — Updated _compose_fov_image and _apply_map_painter_overlay to use combined state maps method
• tests/test_mask_painter_mode_visibility.py — Added TestPainterStateMapsCaching class (5 tests)
• tests/bootstrap.py — Added missing stubs for headless test compatibility

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Tests

python -m unittest tests.test_mask_painter_mode_visibility

• ✅ 41 tests passed