test: Add generic type corner case tests

[abhinav]

The v0.9.0 release added Go 1.26 support
but removed a generic alias test
without replacing the coverage.
These two new test packages
verify the analyzer handles generics correctly.

Package g tests generic struct fundamentals:
basic instantiation, multiple type parameters,
pointers, map/slice contexts,
return-with-error skipping, nested generics,
and self-referencing generic types (Go 1.26).

Package h tests generic aliases
and cross-package usage:
non-generic aliases to instantiated generics,
parameterized aliases forwarding type params,
narrower constraint aliases, chained aliases,
embedded generic types, and direct cross-package
generic struct literals.

[abhinav]

This change is part of the following stack:

• test: Add generic type corner case tests #65 ◀

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