[ty] Fix more generics-related TODOs

[AlexWaygood]

Summary

Address various generics-related TODOs by converting .to_instance() calls into .to_specialized_instance() calls.

Test Plan

Existing mdtests updated.

[AlexWaygood]

this was necessary or some custom-typeshed tests started panicking because they couldn't find Exception and ExceptionGroup in the custom typeshed

[AlexWaygood]

using is_subtype_of rather than is_assignable_to here because I think we should infer BaseExceptionGroup rather than ExceptionGroup if symbol_ty is Unknown or similar

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

hydra-zen (https://github.com/mit-ll-responsible-ai/hydra-zen)
- error[invalid-return-type] src/hydra_zen/wrapper/_implementations.py:945:16: Return type does not match returned value: Expected `DataClass_`, found `@Todo(unsupported type[X] special form) | (((...) -> Any) & dict[Unknown, Unknown]) | (DataClass_ & dict[Unknown, Unknown]) | (list[Any] & dict[Unknown, Unknown]) | dict[Any, Any] | (((...) -> Any) & list[Unknown]) | (DataClass_ & list[Unknown]) | list[Any] | (dict[Any, Any] & list[Unknown])`
+ error[invalid-return-type] src/hydra_zen/wrapper/_implementations.py:945:16: Return type does not match returned value: Expected `DataClass_`, found `@Todo(unsupported type[X] special form) | (((...) -> Any) & dict[Unknown, Unknown]) | (DataClass_ & dict[Unknown, Unknown]) | (list[Any] & dict[Unknown, Unknown]) | dict[Any, Any] | (((...) -> Any) & list[Unknown]) | (DataClass_ & list[Unknown]) | list[Any]`
+ error[type-assertion-failure] tests/annotations/declarations.py:951:5: Actual type `FullBuilds[Unknown] | StdBuilds[Unknown]` is not the same as asserted type `FullBuilds[@Todo(Support for `typing.TypeAlias`)] | StdBuilds[@Todo(Support for `typing.TypeAlias`)]`
- Found 649 diagnostics
+ Found 650 diagnostics