Introduce `unify_matched_overload` to handle type variable propagation
for overloaded functions. This ensures that when an overload is chosen,
its concrete parameter types are unified with the actual argument types.
This is crucial for resolving type variables nested within closures
called through overloaded functions.
Additionally, this commit:
- Allows `series` to infer schema type from `push` calls, simplifying
its signature.
- Adds a fallback to `ValueSeries` in `rtl::series` if schema injection
fails.
- Updates `StaticType::TypeVar` to return `Any` when accessed,
simplifying field access logic.
- Adjusts tests to reflect the simplified `series` signature.
Brummel
d7d1aef8ed