Filter degenerate decomposition cells and short-circuit sweep generation for near-zero-area polygons

[Copilot]

decompose_polygon() could return zero/near-zero-area cells from CGAL decomposition, and forwarding those cells to generate_sweep_pattern() could trigger CGAL orientation errors or numeric failures. This PR adds area-based guards at both boundaries so degenerate polygons are excluded before sweep computation.

• Area thresholds for degenerate geometry handling

  • Added module-level minimum-area constants in trajgenpy/Geometries.py:
    • MIN_DECOMPOSE_POLYGON_AREA = 1.0
    • MIN_SWEEP_POLYGON_AREA = 1.0
  • Documented thresholds as CRS units² and explicitly tied them to degenerate-cell protection.

• Decomposition output filtering

  • Updated decompose_polygon() to filter sub-polygons returned by bindings.decompose(...).
  • Cells with area below MIN_DECOMPOSE_POLYGON_AREA are dropped before return.

• Sweep generation safety guard

  • Updated generate_sweep_pattern() to return [] immediately when polygon.area < MIN_SWEEP_POLYGON_AREA.
  • This prevents below-threshold polygons from reaching bindings.generate_sweeps(...).

• Regression coverage

  • Added tests in tests/test_geometries.py for:
    • filtering of below-threshold cells in decompose_polygon()
    • early empty-return behavior in generate_sweep_pattern() and no call-through to bindings for small polygons

if polygon.area < MIN_SWEEP_POLYGON_AREA:
    return []

polygons_list = [
    shapely.Polygon([(vertex.x, vertex.y) for vertex in polygon])
    for polygon in decompose_polygons
]
return [polygon for polygon in polygons_list if polygon.area >= MIN_DECOMPOSE_POLYGON_AREA]