Added support for serializing IEnumerables & structs.

[robgruen]

This pull request significantly improves the handling of .NET collection, dictionary, and value types during schema export, ensuring that the generated TypeScript schemas more accurately reflect JSON serialization behavior. The changes address previous issues where collections and certain value types (like Guid and DateTime) were incorrectly exported as empty interfaces or leaked internal implementation details. The update also adds comprehensive tests to verify correct schema generation for a wide variety of types.

Improvements to type handling and schema export:

• Added robust detection and handling for array-like (IEnumerable<T>, List<T>, etc.) and dictionary-like (IDictionary<K,V>, Dictionary<K,V>, etc.) types, ensuring they are exported as TypeScript arrays and maps respectively, without leaking internal .NET implementation details. [1] [2] [3] [4] [5] [6] [7]
• Improved mapping of scalar value types that serialize as strings (e.g., Guid, DateTime, DateTimeOffset, DateOnly, TimeOnly) to TypeScript string type, preventing them from being exported as empty interfaces. [1] [2] [3]

Test coverage enhancements:

• Added new test types in Schemas.cs to cover collections, dictionaries, self-referential enumerables, and structs, verifying correct schema export for each case.
• Introduced comprehensive unit tests to ensure correct TypeScript schema generation for the above scenarios, including edge cases such as self-referential enumerables and scalar value types.

These changes collectively make schema generation more robust, accurate, and aligned with how .NET types are serialized to JSON, while also preventing schema bloat and infinite recursion in pathological cases.

Fixes: #218