Remove usage of erased Tags

[hearnadam]

Now that Tag supports low cost subtype checking, we should switch to using it in ContextEffect handling (if not already), then remove usage of erasedTag.

[avasis-ai]

I was looking at how Tags are used across the codebase — is the intent to replace the erased Tags with the new Kyo Tags that carry type information at runtime, or is this about removing the erased keyword usage specifically? The Tag machinery in kyo-prelude seems to already have the non-erased variants, wondering if this is mostly a mechanical find-and-replace or if there are places where the type-level semantics change.