Fuzz test CheckTx vs PrepareProposal

[rootulp]

Context

Related to #4275 except we want to generalize this to all types of transactions. If the tx passes CheckTx then it should pass PrepareProposal.

cc: @evan-forbes

Problem

There may be edge case transactions that pass CheckTx but always fail PrepareProposal. These edge cases are a DoS attack.

Proposal

We could use a fuzz test that txs verifies that if the tx passes CheckTx then it also must be able to be included in an empty block (i.e. a block where it is the only tx).

If we use txsim for creating the transactions, then we may need to modify txsim to create multiple transactions from the same account in one block to uncover more edge case transactions.