[ty] Revert deferred call-gate optimization (#26792)
## Summary
This reverts #26775 after [a post-merge
finding](https://github.com/astral-sh/ruff/pull/26775#issuecomment-4964970253)
showed that deferred call gates are dropped too early at nested
control-flow merges. An unrelated nested `if` can therefore discard a
preceding `Never` call gate and allow narrowing from an unreachable path
to widen the final type.
We restore the previous eager call-gate materialization while we
continue the optimization in a separate draft PR.
