Expand Python/Colab demos to explicitly cover concave, holes, and 2D partition workflows

[Copilot]

The current PR still read as mostly single-convex-polygon plotting in Colab/demo flows. This update makes the key implicit-spline use cases explicit and discoverable: convex evolution, concave/freeform polygons, polygons with holes, and multi-polygon 2D partitions.

• Demo restructuring (examples/demo.py)

  • Reorganized into 4 explicit sections:
    • Convex polygons
    • Concave / freeform polygons
    • Polygons with holes
    • Collections forming a 2D partition
  • Added explicit concave examples:
    • single concave polygon contour
    • paper-style multi-panel contour evolution under varying delta
  • Kept/expanded hole and partition examples with clearer sequencing and labels:
    • hole compositions (single and multiple holes)
    • hole-specific delta evolution panel
    • partition net + summed basis surfaces + per-cell basis gallery

• Colab-visible notebook coverage (notebooks/01_basic_polygon.ipynb)

  • Extended notebook beyond convex basics with runnable sections for:
    • concave/freeform polygon demos
    • polygons with holes
    • multi-polygon 2D partition basis/sum visualization
  • Updated imports and section flow so these features are visible in normal notebook execution, not buried in helper-only paths.

• Example discoverability docs (examples/README.md)

  • Updated feature map to explicitly call out convex, concave, holes, and partition demos.
  • Updated notebook description to reflect Colab-visible coverage.

Example of the new explicit concave panel call:

fig = panel_delta_shapes(
    P_concave,
    deltas=(0.05, 0.10, 0.16, 0.24, 0.34, 0.46),
    n=2,
    N=320,
    layout=(2, 3),
    title="Concave polygon: contour evolution under increasing $\\delta$",
)

[Copilot]

Pull request overview

This PR expands the Python demo script and Colab-visible notebook to explicitly showcase additional implicit-spline workflows beyond convex polygons—specifically concave/freeform polygons, polygons with holes, and multi-polygon 2D partition visualizations—while updating the examples README to improve discoverability.

Changes:

• Restructures examples/demo.py into four feature-focused sections and adds explicit concave/freeform polygon figures plus clearer holes/partition sequencing.
• Extends notebooks/01_basic_polygon.ipynb with runnable concave, holes, and 2D partition sections and updates imports accordingly.
• Updates examples/README.md to reflect the expanded demo/notebook coverage.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
notebooks/01_basic_polygon.ipynb	Adds concave, holes, and partition demo sections and visualization helpers for Colab-visible execution.
examples/README.md	Updates the examples feature map and notebook description to surface concave/holes/partition demos.
examples/demo.py	Reorganizes the standalone demo into explicit feature categories and adds concave polygon + panel examples.

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