## Description 

PTBs can only have `TransferObjects` or `MergeCoins` following a command
that uses `Random`, enforced by validators when receiving a signed transaction.

## Test Plan 

New transactional tests

---
If your changes are not user-facing and do not break anything, you can
skip the following section. Otherwise, please briefly describe what has
changed under the Release Notes section.

### Type of Change (Check all that apply)

- [x] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [x] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes
PTBs can only have `TransferObjects` or `MergeCoins` following a command
that uses `Random`, enforced by validators when receiving a signed transaction.