Support sendBatch calls in web3c

[willscott]

Currently, the provider only intercepts individual calls, and not call batches. It's unclear if the eth.Contract interface will trigger batches of calls, but the underlying pub key and confdiential calls are still worth hooking in the provider if they get mixed into a batch use case.

• Develop test case exercising batch functionality

[willscott]

The semantics of sendBatch is the clients saying "i want these operations to happen in this order". if they are sent as independent web3 calls, there's a potential for re-ordering, or that an operation will get canceled while later ones still occur.

it's still possible that only some initial subset of the batch actually execute.