feat(modeling): preserve color for offset and extrude

[platypii]

This PR preserves the color attribute when applying operations like offset and extrude and project.

This seems like a clear improvement for users of JSCAD. If you have a 2D object with color like on the left, would you expect extrusion to preserve the color? Or lose it?

preserve-color.js

import * as jscad from '@jscad/modeling'
const { colorize } = jscad.colors
const { extrudeLinear } = jscad.extrusions
const { square } = jscad.primitives
const { translate } = jscad.transforms

export const main = () => {
  const obj2d = [
    colorize([1, 0, 0], square({ center: [0, -4] })),
    colorize([0, 1, 0], square({ center: [0, 0] })),
    colorize([0, 0, 1], square({ center: [0, 4] })),
  ]
  return [
    translate([-4, 0], obj2d),
    translate([4, 0, 0], extrudeLinear({}, obj2d)),
  ]
}

If someone really want no color, it's easy to remove using colorize. But if you want to preserve color of sub-components through an operation... there's really no good way to do it without this change.

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Does your submission pass tests?

[hrgdavor]

This a move in right direction. Colors from boolean ops were removed for perf gain, but it is possible we will be able to make keeping colors optional in the future for booleans.

[z3dev]

@platypii nice set of changes, and very nice improvements for the user experience.

i just have a bunch of nits. sorry.

[platypii]

@z3dev I just pushed some more changes which I hope will address your concerns:

• returns new geometries even if the shape is the same
• handles empty geometries when it makes sense
• added tests for the above
• addressed other PR feedback (function and variable names)

Let me know what you think

[z3dev]

@platypii thanks for hanging in there. Sometimes it take time to sort out differences in opinion.

The changes are all good now, with improvements everywhere.