Runtimes should expose a CheckTx API

[kostko]

Runtimes should expose a CheckTx API that allows the worker host to request runtime-specific light-weight transaction checks and immediately reject transactions if these checks fail (similar to Tendermint's CheckTx).

This can be used by the leader to reject transactions early before dispatching them to the compute committee. It may make sense to use a separate runtime instance to perform these checks to not block the main runtime from doing work while performing checks.

[peterjgilbert]

Runtimes should also expose an API to order transactions within a batch. This is needed if we want to be able to process multiple transactions from a given sender within a batch, as the Ethereum nonce must match exactly. Note this also requires batch ordering to be preserved across batch submission--not sure whether we guarantee this currently.