[invariant] streaming swaps
- Updates the asgard module invariant to account for streaming swaps. That invariant is only for the native coin balances (external asset/vault coins will be a new/updated invariant coming soon).
- Adds a streaming_swaps invariant which makes sure the streaming swap records correspond to the swap queue and the values are sane.
- Adds a minimal native streaming swap regtest which was necessary to test the invariant.