Remove coerce.js function pass-through hack; fatal errors on unknown marker symbols

[Copilot]

The codebase had a special-case in coerce.js allowing raw JS functions to bypass enumerated value validation (added for custom marker symbols), and all symbol lookup failures silently fell back to symbol 0 (circle) with no indication of the bad input.

Changes

• src/lib/coerce.js: Remove the typeof v === 'function' bypass in enumerated coercion. Functions are now treated as invalid and fall back to the attribute default like any other unrecognized value.

• src/components/drawing/index.js:

  • symbolNumber(v): throws Error('Unknown marker symbol: ...') instead of returning 0
  • singlePointStyle(...): throws on null lookupSymbol result instead of silently falling back to lookupSymbol(0)
  • applyBackoff(...): throws on unrecognized end-marker symbol; preserves b = 0 when endMarker is legitimately absent

• src/traces/scattergl/convert.js — getSymbolSdf(...): throws on null lookupSymbol result instead of crashing later with a cryptic Cannot read property 'path' of null

Before / after behavior:

// Before: silently rendered a circle (symbol 0)
marker: { symbol: 'typo-symbol' }

// After: throws immediately
// Error: Unknown marker symbol: typo-symbol

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[gatopeich]

@copilot OO encapsulation: The Error should be thrown from inside lookupSymbol

[Copilot]

@copilot OO encapsulation: The Error should be thrown from inside lookupSymbol

Done in b9a942c. lookupSymbol now throws Error('Unknown marker symbol: ...') directly for every unrecognised input, and the null-check boilerplate has been removed from all call sites.