break(helpers) tighten geometry() coordinates typing

[modusensus]

Summary

Tightens the coordinates parameter of geometry() so TypeScript enforces the correct coordinate shape for each geometry type at compile time:

• "Point" → Position
• "LineString" / "MultiPoint" → Position[]
• "Polygon" / "MultiLineString" → Position[][]
• "MultiPolygon" → Position[][][]

Resolves #2973

Breaking change

⚠️ Compile-time only — no runtime behavior change. Call sites passing arrays with the wrong nesting depth (or other loose arrays) will now fail type checking. This follows the type-strictness direction of #3160–#3163.

Design notes (open to feedback)

• CoordinatesFor<T> is deliberately not exported. Exporting it would add a conditional type to the public API that the docs generator cannot resolve (it renders as Type: any in the README). If you'd prefer it exported for downstream generic code, that's a one-line change — happy to flip it.
• GeometryType is exported because it resolves cleanly in the generated docs, and it gives consumers a reusable name for the six geometry kinds geometry() accepts. The name is bikesheddable (GeometryTypeName, GeometryTypeString, …).
• The documentation generator renders parameter types from the TypeScript signatures rather than the @param annotations, which is why the README shows coordinates as CoordinatesFor<T> instead of a Position|Position[]|… union.

Changes

• New exported GeometryType union and internal CoordinatesFor<T> conditional type in @turf/helpers
• geometry()'s runtime logic is unchanged; a single re-broadening alias bridges the deferred generic to the per-type constructors in the switch
• Positive and negative type assertions added in packages/turf-helpers/types.ts (the package's existing test:types convention)
• README regenerated via pnpm run docs
• Added my details to @turf/helpers' contributors field per the PR checklist

Checklist

• Meaningful title, including the name of the package being modified
• Summary of the changes
• Heads up if this is a breaking change
• Issue this resolves: Increase type strictness of @turf/helper's geometry() coordinates #2973
• Inclusion of my details in the contributors field of package.json
• Confirmation I've read the steps for preparing a pull request

Full pnpm -r run test passing locally across all 122 packages (the root lint suite could not run on this Windows machine due to a monorepolint Windows path bug — CI will cover it).