Chuanqiu He

Adding sync_wait_with_variant

9

## Any background context you want to provide? P2300R5: [sync_wait_with_variant](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2300r5.html#design-typed) sync_wait_with_variant, which accepts any sender, but returns an optional whose value type is the variant of all the possible tuples...

Integrating sync_wait & sync_wait_with_variant

3

## Proposed Changes: Ref: [P2300R5](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2300r5.html#example-schedulers) Integrate sync_wait and sync_wait_with_variant. ## Checklist - I have added a new feature and have added tests to go along with it.