feat: add basic support for projections

[lubianat]

a step towards #41, simpler than true volumetric rendering

note: some support of Claude Opus 4.8; code reviewed manually

the API is like:

img.render({
    projection: "max", 
    projectionAxis: "x", 
    maxVoxels: 8_000_000 // optional, defaults to 64_000_000
})}

chunks are projected individually, so LUTs, autoBoost and similar should work normally

steps:

• create draft
• test manually (different scenarios)
• add tests
• update documentation

sample (in index.html):

edit: comparison with the current default renderings:

[will-moore]

Thanks for the PR, I'll look in detail next week...