* updates ScanTask.subscribe() to return rsp_tx instead of awaiting it, returns service errors from grpc methods
* Adds a timeout to scan service and improves error message when subscribe responders are dropped
* Returns an error from `RegisterKeys` svc request when no keys are registered
* tests register keys error message
* Adds test for timeouts
* adds TODOs for fixing bugs
* Orders scan service requests in scan method
* removes CheckKeyHashes request
* fixes bad merge conflict resolution
* update test to check downcast to Elapsed error
* update errors in scan method
* update error msg in register_keys method
* fixes compiler error
* merges scan task tests and checks that the scan task removes keys
* Adds test to CI
* Skip to expected block height and assert that the result is from that height
* Updates test docs and uses zebrad state path for scan cache
* Log "Zcash network: {network}" from scan task commands test
Arya