fix(parser): validate HIR return annotations

[zhen8838]

Why

• HIR return annotations were parsed but did not validate the inferred body result, allowing real dispatch variants to silently disagree with their declared return contract.

What

• Validate annotated HIR function bodies and dispatch variant bodies with types_compatible.
• Require a return annotation on pass dispatch prototypes and support recursive tuple[...] return annotations.
• Add a diagnostic regression test and make the decode fixture explicitly materialize its declared GMEM result.
• Remove unrelated ordinary-function annotations whose bodies intentionally remain SMEM or UMAT.

Contract

• Omitted Tensor[...] storage remains GMEM; it is not a wildcard.
• Ordinary functions keep body.type as their IR return type after validation. Dispatch variants keep the exact prototype return type.

Risk

• Existing authored return annotations now need to describe the body result. The full source suite passes after updating the affected fixtures and tests.