Port MathJax 3.2.2 to native Go

[alixander]

Summary

• port the MathJax 3.2.2 TeX-to-SVG pipeline used by D2 to native Go
• preserve the exact D2 package surface, MathML structure, SVG serialization, measurements, font metrics, glyph paths, and error rendering
• expose stateless Render, RenderWithOptions, and Measure APIs with no production JavaScript runtime
• document exact upstream provenance and Apache/MIT licensing
• add pure-Go, race, Go-floor, WASM, and pinned frozen-oracle CI

Compatibility

This targets the custom MathJax 3.2.2 component frozen in D2, including base, mathtools, ams, amscd, braket, cancel, cases, color, gensymb, mhchem, and physics. JavaScript is used only by the optional external differential oracle and is not embedded in the library.

The suite freezes 31 D2 formulas, 107 selected handler render cases, 42 MathML definitions, 2,373 glyphs, 119 delimiters, and the mhchemParser 4.1.1 corpus.

Validation

• GOWORK=off go test ./...
• GOWORK=off go test -race ./...
• GOWORK=off go vet ./...
• GOWORK=off GOTOOLCHAIN=go1.23.12 go test ./...
• GOOS=js GOARCH=wasm GOWORK=off go build ./...
• full SHA-pinned D2 MathJax differential oracle

D2 integration

Linked draft: d2lang/d2#2824