refactor: update test references for TaskManager (WIP - 24 failures remain)

Update TestProtocol interface and all test references to access
task state through protocol.tasks instead of directly on Protocol.

Remaining 24 failures fall into 3 categories:
1. Progress + tasks (2): CreateTaskResult detection needs verification
2. requestStream (8): Tests create Protocol without TaskManager
3. Error handling (14): Tests need TaskManager for resolver access

All are test-only issues - source code compiles and typechecks cleanly.

Author: felixweinberger