feat: add ColumnShapeExtension with per-instance bevel and radius support

[Copilot]

Background

Ports ExperimentalColumnLayer functionality from deck.gl-community#470 / deck.gl#9933 as an extension per Chris Gervant's recommendation.

Adds per-instance bevel shapes (dome, cone, flat) and radius scaling to ColumnLayer for hierarchical/tree visualizations.

Change List

• modules/extensions/src/column-shape/column-shape-extension.ts — Extension class with getBevel and getRadius accessors
• modules/extensions/src/column-shape/shader-module.ts — Shader injection for vertex position modification based on bevel params
• modules/extensions/src/index.ts — Export new extension and types
• test/modules/extensions/column-shape.spec.ts — Unit tests including edge cases (negative values, partial objects, zero radius)

Usage

import {ColumnLayer} from '@deck.gl/layers';
import {ColumnShapeExtension} from '@deck.gl/extensions';

new ColumnLayer({
  data: hierarchicalData,
  getPosition: d => d.position,
  getElevation: d => d.height,
  getRadius: d => d.radiusScale,  // Per-instance radius multiplier
  getBevel: d => {
    if (d.isLeaf) return 'dome';     // Rounded top
    if (d.isBranch) return 'cone';   // Pointed top
    return {segs: 5, height: 100, bulge: 0.2};  // Custom params
  },
  extensions: [new ColumnShapeExtension()]
});

Bevel types: 'flat' (default), 'dome', 'cone', or {segs, height, bulge} for full control.

Original prompt

Open up a PR with a new extension called ColumnShapeExtension that applies the changes intended in visgl/deck.gl-community#470 but as an extension rather than as a new layer - as recommended by Chris Gervant - reference this PR as well as the original PR. Were going full circle

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[charlieforward9]

Superseded: visgl#10003