fix(types): type geo_distance_meters as a field-name map

[cpruijsen]

SearchResponseHit.geo_distance_meters is now { [key: string]: number }, keyed by the collection's geopoint field.

Fixes #348.

{ location: number } matched the geosearch docs example only because that collection's field is named location. A coordinates geopoint returns { "coordinates": 95432 } and did not type-check.

Decision

• Chose: { [key: string]: number }
• Alternative: { [TAttribute in keyof T]?: number } (same pattern as SearchResponseHighlight)
• Why: Client.collections() defaults T to object, and keyof object is never, so a mapped type would make .location a type error on the untyped path the docs use. The issue asked for a string index signature first.

Test plan

• pnpm typecheck fails without the source change and passes with it (test/geo_distance_meters.type.test.ts)
• coordinates type-checks on a document that declares that field
• coordinates and location type-check on the default document generic (object)