[harshiltewari2004]

Resolves #9252

Changes:

• replaceBinaryOperator (src/strands/strands_transpiler.js) now maps ** to pow, so a ** b becomes a.pow(b). This also covers **=, since compound assignments go through the same function.
• Adds StrandsNode.prototype.pow (src/strands/strands_api.js), which builds a pow() function call node rather than a binary operator, since GLSL and WGSL have no ** operator. This resolves the TODO.
• Adds a default case that throws a strands error naming the operator (e.g. &, <<), instead of crashing with .undefined is not a function / reading 'startsWith' inside the transpiler. This was the second option in the issue; happy to drop it into a separate PR if you'd rather keep this one to ** only.

Tests (new exponentiation operator (#9252) suite in test/unit/webgl/p5.Shader.js):

• v ** 2 renders the same as pow(v, 2)
• v **= 2 works
• an unsupported operator throws unsupported operator

All three failed before the source change and pass after. The change is in the backend-independent transpiler, so I only added WebGL tests; happy to add WebGPU ones too.

npx vitest run: everything passes except test/unit/webgpu/p5.Shader.js → "handle passing a value from a vertex hook to a fragment hook with swizzle assignment", which also fails on a clean main.

PR Checklist

• npm run lint passes
• [Inline reference] is included / updated — N/A, no public API change
• [Unit tests] are included / updated