[Task architecture] - Make `TaskState` object safe

[ss-es]

What is this task and why do we need to work on it?

To make stopping/restarting tasks more uniform, the TaskState trait needs to be made object safe.

What work will need to be done to complete this task?

There are a lot of constraints imposed by existing code (particularly our integration tests), and a large part of the work will be disentangling the varying implementations of the existing TaskState trait that are currently spread throughout our code for various different kinds of tasks.

Are there any other details to include?

No response

What are the acceptance criteria to close this issue?

TaskState is object safe.

Branch work will be merged to (if not the default branch)

No response