fixes #22936; Generic inheritance matching gives type mismatch when object has members

[ringabout]

fixes #22936

This pull request improves the compiler's handling of generic type constraints, specifically for subtypes of generics, and adds a test to cover this behavior. The main changes are an enhancement to the type relationship logic in the compiler and a new test case for generic subtyping with Future.

Compiler improvements for generic subtyping

• Updated typeRel in compiler/sigmatch.nim to allow generic constraints (like F: Future) to accept not just direct instantiations but also descendants of the generic family, ensuring more flexible and correct overload resolution. Inheritance depth is now considered for overload ranking, making deeper descendants slightly less preferred, consistent with other inheritance-based matches.

New test coverage

• Added a test in tests/typerel/t8905.nim to verify that generic constraints correctly accept subtypes of Future, including a custom B[T, E] = ref object of Future[T] type, and that overloads like take, takeMany, and the macro checkFutures work as expected with these types.

[Copilot]

Pull request overview

This pull request fixes issue #22936 by improving the compiler’s type relationship logic so generic constraints (e.g. F: Future) accept not only direct instantiations (Future[T]) but also subtypes/descendants of that generic family, and by adding a regression test covering the scenario.

Changes:

• Extend typeRel handling for tyGenericBody constraints to recognize descendant types via isGenericSubtype, not just direct tyGenericInst matches.
• Incorporate inheritance depth into overload ranking for these generic-family descendant matches (deeper descendants become slightly less preferred).
• Add a regression test ensuring generic constraints accept subtypes of Future[T] even when the object has members, including through a macro signature.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
compiler/sigmatch.nim	Updates typeRel for tyGenericBody constraints to accept generic-family descendants and apply inheritance-based ranking penalties.
tests/typerel/t8905.nim	Adds a regression test for generic subtyping with Future[T] descendants (including macro parameter matching).

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