Schema inference: resolve string annotations, Annotated and NewType; give item params their real name #27

Follow-up of #19 (PR #26). Annotation-based type inference still gives 'string' for: string annotations (everything under from __future__ import annotations; resolve with typing.get_type_hints / i2 Sig), Annotated[list[int], ...] (unwrap), NewType (use __supertype__). Also: when inferring items, a custom param_to_prop_type receives a Parameter named _ rather than the owning parameter's name.