[Fix] Futures in Tuples

[evan-schott]

Fixes #28312

Design choices:

• Using eq_flat_relaxed over eq_flat in TYC:
  • ST makes sure that if we have multiple structs of the same name, then there is an error (before TYC starts).
  • eq_flat for strict equality, eq_flat_relaxed for relaxed equality. (When future is not explicit or struct matches but program origin is different).
• For change we could use .eq_flat_relaxed instead of self.check_eq_types but I thought it would be nice to have consistent usage of check_eq_types throughout TYC.