Add native perspective projection mode and tests

[RaulDurand]

This PR adds a native perspective projection mode to CeTZ and includes docs/tests for it.

#cetz.canvas({
  import cetz.draw: *

  perspective(x: 28deg, y: -35deg, distance: auto, {
    on-xz({ rect((-1, -1), (1, 1)) })
    line((0, 0, 0), (1, 1, 1), stroke: red)
  })
})

What’s included

• Added draw.perspective(...) in src/draw/projection.typ
• Exported perspective from src/draw.typ
• Added API docs page:
  • docs/api/draw-functions/projections/perspective.mdx
  • docs/api/sidebar.js entry under Projections
• Added projection regression test:
  • tests/projection/perspective/test.typ
  • tests/projection/perspective/ref/1.png

Perspective behavior

• Uses the same default camera angles as ortho (x: 35.264deg, y: 45deg, z: 0deg)
• Applies perspective divide with internal near/depth handling
• Computes and uses a reference depth (d_ref, corresponding to the nearest depth) to anchor projection scale:
  • projected coordinates use x' = d_ref * x / w, y' = d_ref * y / w
  • with w = max(-z, near) in view space
• At the reference depth (the nearest visible depth in camera space), projected lengths are approximately preserved because scale is anchored to that plane; objects farther in depth are progressively smaller, which helps keep deep scenes from overflowing the canvas.
• distance controls camera distance and therefore perspective strength:
  • smaller distance => stronger perspective (more foreshortening)
  • larger distance => flatter look (closer to orthographic)
• distance is internally constrained to stay in front of the nearest geometry, preventing extreme camera placements that would cause distorted projections.
• distance: auto derives a stable value from scene depth
• Supports sorting and cull-face options like existing projection paths
• Mark handling in perspective forces transformed-shape placement, avoiding oversized/distorted marks/arrows.

Validation

• tt run projection/perspective projection/ortho mark/shape/transform
• All passed locally.

[johannes-wolf]

This is great! Thank you. :)
Some small things…