Adds 58 tests covering lifecycle events, activity translation, config
buffering, session state persistence, auth setup, error handling, abort,
and concurrent send() guard for both new protocol implementations.
Also fixes a timing bug in RemoteSubagentProtocol where _sessionState was
persisted in a finally block, causing it to be written after the result
promise settled. Moved _saveSessionState() calls to run synchronously
before each _resultResolve/_resultReject so callers see updated
contextId/taskId immediately after getResult() settles.
Adam Weidman