Preserve collection toJSON return types - #242

Direct ArraySchema.toJSON() and MapSchema.toJSON() calls currently return any[] and any, allowing invalid assignments and losing the serialized element shape in typed UI state.

Annotate the existing methods with arrays/string-keyed records of each element's inferred toJSON() return type, or the element type when it has no serializer. This preserves primitive and literal values, recursively serialized Schema data, and custom toJSON() overrides. Keep the existing ToJSON utility, Schema/assign behavior, and runtime implementation unchanged.

Extend the strict emitted-declaration fixtures with positive and negative checks for primitive values, codec-named string literals, Schema data versus class methods, nested/custom serialization, union/default values, recursive collections, and native collection interfaces. The latter two cover the compatibility problems discussed in #174.

Validation on Node.js 20 and 24:

• npm test: 1,043 passing, one existing pending; all six TypeScript 5/7 compiler configurations pass.
• npm run build and npm run test:exports pass.
• The exact new consumer fixtures fail against the unmodified serializers on both compilers; the four unaffected configurations pass.
• All 6 emitted JavaScript runtime artifacts are byte-identical to the unmodified build.

Fixes #162