* Refactor to create `verify_sprout_shielded_data`
Move the join split verification code into a new
`verify_sprout_shielded_data` helper method that returns an
`AsyncChecks` set.
* Test if signed V4 tx. join splits are accepted
Create a fake V4 transaction with a dummy join split, and sign it
appropriately. Check if the transaction verifier accepts the
transaction.
* Test if unsigned V4 tx. joinsplit data is rejected
Create a fake V4 transaction with a dummy join split. Do NOT sign this
transaction's join split data, and check that the verifier rejects the
transaction.
* Join tests to share Tokio runtime
Otherwise one of the tests might fail incorrectly because of a
limitation in the test environment. `Batch` services spawn a task in the
Tokio runtime, but separate tests can have separate runtimes, so sharing
a `Batch` service can lead to the worker task only being available for
one of the tests.
fdeb6d5ec8