Improve error message for non-numeric strands construction (#9218) - #9229

Addresses #9218

Changes

Improves the error thrown in mapPrimitiveDepsToIDs (src/strands/ir_builders.js) when a non-numeric value is passed into a scalar or vector construction.

Previously, the error stringified the raw value. In the case from #9218 (using filterColor directly instead of filterColor.texCoord), this dumped the internal hook callback's source code into the message.

Now the error:

• Detects when the offending value is a function or object rather than a primitive
• Describes it in plain terms (e.g. "a function") instead of stringifying it, which avoids the raw source dump
• Adds a hint when the value looks like a strands hook or variable used directly, rather than a property on it

Before / after

Before (from #9218):

[p5.strands type error]: You've tried to construct a scalar or vector type with a non-numeric value: function(hookUserCallback) {
  const args = setupHook();
  hook._result = hookUserCallback(...args) ?? hook._result;
  finishHook();
}

After:

You've tried to construct a scalar or vector type with a non-numeric value: a function
This looks like a shader hook or strands variable used directly, rather than a property on it (e.g. you wrote `filterColor` instead of `filterColor.texCoord`).

Scope

This covers only the "better error content at the throw site" part of #9218. The following are left as follow-up work:

• Filtering internal strandsNode frames out of the stack trace
• Source mapping from transpiled code back to the original sketch lines

Tests

Adds a regression test in test/unit/webgl/p5.Shader.js that reproduces the filterColor * 30 mistake from the issue and asserts on the new message. The full p5.Shader suite passes (161/161).

PR Checklist

• npm run lint passes
• [Inline reference] is included / updated (N/A: no public API or docs changes)
• [Unit tests] are included / updated