Prevent UI scopes from canceling transactions (EXPOSUREAPP-2312) (#1093)

* Don't execute the transactions as part of any view scopes.
We don't want to cancel them if the viewscope is cleared.

This commit introduces distinct scopes for each transaction.

* Mock injection helper behavior on existing tests.

* Simplify to one CoroutineScope for all Transaction.
Switch context when awaiting the transaction codeblock to end,
otherwise a cancellation still affects us.

* Add test for timeout

* Remove unused code.

* Expand comment on unexpected test behavior

* Even without actual timeout, runBlockingTest causes flaky test behavior.

Co-authored-by: Matthias Urhahn <matthias.urhahn@sap.com>
Co-authored-by: Jakob Möller <jakob.moeller@sap.com>