feat: cache loaded fonts

[tybulewicz]

What does this PR do?

This pull request implements font caching to optimize performance when rendering visualizations with many detections on large images. The solution addresses issue #484 by using functools.lru_cache to cache ImageFont objects, preventing repeated expensive font loading operations.

Fixes #484

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[Copilot]

Pull request overview

This pull request implements font caching to optimize performance when rendering visualizations with many detections on large images. The solution addresses issue #484 by using functools.lru_cache to cache ImageFont objects, preventing repeated expensive font loading operations.

Changes:

• Added two new cached utility functions (default_font and truetype_font) in src/model_api/visualizer/utils.py using @lru_cache(maxsize=5) decorator
• Updated all visualizer primitives (BoundingBox, Label, Keypoints, Overlay) to use the new cached font functions instead of directly calling ImageFont.load_default() or ImageFont.truetype()
• Reorganized imports in scene files to import get_label_color_mapping from model_api.visualizer.utils instead of model_api.visualizer.scene.utils

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/model_api/visualizer/utils.py	Added default_font and truetype_font cached utility functions with LRU cache
src/model_api/visualizer/primitive/bounding_box.py	Updated to use cached default_font function
src/model_api/visualizer/primitive/label.py	Updated to use cached default_font and truetype_font functions
src/model_api/visualizer/primitive/keypoints.py	Updated to use cached default_font function
src/model_api/visualizer/primitive/overlay.py	Updated to use cached default_font function
src/model_api/visualizer/scene/detection.py	Updated import path for get_label_color_mapping
src/model_api/visualizer/scene/segmentation/instance_segmentation.py	Updated import path for get_label_color_mapping

Comments suppressed due to low confidence (5)

src/model_api/visualizer/utils.py:8

• The copyright header should appear before the imports. The codebase convention is to have the module docstring first, then the copyright header, and then the imports.
  src/model_api/visualizer/utils.py:48
• Missing return type annotation. The function should specify its return type, such as ImageFont.FreeTypeFont or the appropriate type from PIL. The codebase uses return type annotations for similar functions (e.g., get_label_color_mapping on line 34 has -> dict[str, str]).
  src/model_api/visualizer/utils.py:61
• Missing return type annotation. The function should specify its return type, such as ImageFont.FreeTypeFont or the appropriate type from PIL. The codebase uses return type annotations for similar functions (e.g., get_label_color_mapping on line 34 has -> dict[str, str]).
  src/model_api/visualizer/utils.py:67
• Missing Returns section in the docstring. The docstring should include a Returns section that describes the return value, similar to the default_font function above (lines 54-55) which documents "A PIL ImageFont instance with the default font and specified size."
  src/model_api/visualizer/utils.py:69
• The new cached font functions default_font and truetype_font lack test coverage. Since the visualizer module has comprehensive test coverage (see tests/unit/visualizer/test_primitive.py), consider adding tests to verify that the caching mechanism works correctly. The tests should verify that repeated calls with the same parameters return the same cached object, and that different parameters return different objects.

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