Add shader examples for math functions

[SOUMITRO-SAHA]

Resolves #8777 (Calculation batch)

Changes:

Adds inline p5.strands examples to the reference documentation for 13 calculation functions in src/math/calculation.js:

• abs() — mirror/fold effect using abs(sin(t))
• ceil() — stepped color bands
• floor() — posterized banding effect
• fract() — repeating gradient pattern
• sqrt() — smooth easing curve
• pow() — gamma curve effect
• exp() — accelerating brightness
• log() — decelerating color transition
• min() — maximum brightness clamp
• max() — minimum brightness clamp
• round() — quantized posterized colors
• lerp() — color blending (maps to GLSL mix)
• map() — remapped time to color

Each example uses buildColorShader() with finalColor.begin()/end() and includes a brief explanation that the function can be used in shaders with p5.strands.

Screenshots of the change:

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated

[nbogie]

looks good though i didn't test the examples.

[nbogie]

As elsewhere, i think breaking this down is clearer

let mixFraction = ...
//define the two colours we'll mix between
//both as [r, g, b, a], all from 0.0 to 1.0
let color1 = [0, 0.8, 08, 1]
let color2 = [1, 0.5, 0.3, 1]
let mixedColor = lerp(color1, color2, mixFraction);
finalColor.set(mixedColor);

This is also has quite a lot going on in order to demonstrate lerp: (millis and sin, and its normalization), but:

• I think it's ok, if we're assuming the expected reader already understands lerp from a 2d context.
• Otherwise a static form like `

//mix a color 25% cyan, 75% magenta
let mixedColor = lerp(cyan, magenta, 0.25);

would be better suited.

However, your example is far more inspiring! I like it!

[SOUMITRO-SAHA]

Thanks @nbogie ! I'll apply the same pattern as PR #8801 — breaking down the lerp() example with named color variables and a clearer structure. I like keeping the animated example since it's more inspiring, but I'll make it more readable.

Pushing the changes shortly!