Modernize proj4 CRS, axis, and datum-grid support

[ibgreen-openai]

Goals

• Modernize @math.gl/proj4 so current CRS definitions and datum transformations can support high-precision geospatial visualization workflows.
• Preserve the existing bound, unary projection API while exposing modern axis-order and grid-registration capabilities.

Changes

• Upgrade proj4 from 2.6.2 to 2.20.9, update wkt-parser, and remove obsolete @types/proj4 because upstream now ships its own declarations.
• Accept WKT2 and PROJJSON CRS definitions, including PROJJSON aliases; export structural projection-definition and options types that do not leak optional upstream geotiff declarations.
• Expose automatic WGS84 UTM definitions (EPSG:32601–32660, EPSG:32701–32760) and UPS definitions (EPSG:5041, EPSG:5042) without manual registration.
• Add constructor-level enforceAxis support and Proj4Projection.registerDatumGrid(...) for synchronous NTv2 datum-grid registration.
• Document modern CRS formats, axis order, and datum-grid usage.
• Add coverage for WKT2, PROJJSON, UTM, UPS/polar stereographic, standalone bound callbacks, and a synthetic NTv2 grid without external binary fixtures.
• Update inherited Hotine Oblique Mercator fixtures to the correct Azimuth Center variant and explicitly request +approx for spherical Transverse Mercator, matching modern proj4 semantics.

Verification

• yarn build — all monorepo packages and generated declarations pass.
• yarn test node — 2,746 / 2,746 assertions pass.
• Focused @math.gl/proj4 suite — 270 / 270 assertions pass.
• yarn test ci — 2,749 / 2,749 headless-browser assertions and 2,746 / 2,746 coverage-enabled Node assertions pass.
• yarn lint — repository formatting and lint checks pass.
• (cd website && yarn build) — production documentation website builds successfully.
• A strict downstream TypeScript consumer compiles published declarations with skipLibCheck: false and without geotiff installed.
• tspc --noEmit --project modules/proj4/tsconfig.json passes.

Compatibility notes

• project and unproject remain bound unary methods, so existing Array.map(projection.project) usage continues to work.
• Modern proj4 distinguishes center-based and natural-origin Hotine variants; fixture definitions now explicitly identify the variant matching EPSG:2057.
• GeoTIFF datum grids remain an optional upstream capability; this wrapper exposes synchronous NTv2 ArrayBuffer registration without introducing a geotiff dependency.