Split painter.py into smaller modules

[bjmorgan]

Summary

Splits rendering/painter.py (1035 lines) into three focused modules (closes #56):

• precompute.py (389 lines) — scene construction: _PrecomputedScene, _PolyhedronRenderData, _precompute_scene, _apply_slab_clip, _collect_polyhedra_faces
• painter.py (514 lines) — scene drawing: projection, depth sorting, painter's algorithm, PolyCollection assembly
• axes_widget.py (172 lines) — crystallographic axes orientation widget (same pattern as legend.py)

Pure move refactor — no logic changes. Also removes a dead from typing import Any import.

[Copilot]

Pull request overview

Refactors the rendering subsystem by splitting the previously monolithic rendering/painter.py into smaller, single-responsibility modules, aligning with issue #56’s separation of concerns (precomputation vs. drawing vs. widgets) while keeping behavior the same.

Changes:

• Introduces rendering/precompute.py containing scene precomputation + slab-clip/polyhedra face collection helpers previously in painter.py.
• Introduces rendering/axes_widget.py containing the crystallographic axes corner widget previously in painter.py.
• Updates renderer call sites and tests to import _precompute_scene (and related helpers) from hofmann.rendering.precompute.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/hofmann/rendering/precompute.py	New module housing view-independent scene precomputation and polyhedra-related helpers.
src/hofmann/rendering/axes_widget.py	New module containing the axes-orientation widget drawing routine.
src/hofmann/rendering/painter.py	Slimmed to focus on projection/depth sorting and drawing; now imports helpers from the new modules.
src/hofmann/rendering/interactive.py	Updated imports to pull _precompute_scene from rendering.precompute.
src/hofmann/rendering/animation.py	Updated imports to pull _precompute_scene from rendering.precompute.
tests/test_rendering/test_painter.py	Updated imports for moved precompute/polyhedra helpers.
tests/test_rendering/test_animation.py	Updated import for moved _precompute_scene.

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