* Fix ImapIdleChA for scheduling race condition
The IMAP IDLE is long-lived process and can be blocked
waiting for any reply from the server.
This way it is not suited to be used in a `TaskScheduler`
especially when it has only one thread in its pool in Spring Boot by default.
Another concurrent scheduled task is exactly an `ImapMailReceiver.IdleCanceller`.
With a single thread in a `TaskScheduler` pool it cannot be reached
therefore we never cancel and IDLE task and cannot react to the connection loss properly
* Rework the `ImapIdleChannelAdapter` logic to use a regular `Executor` and `while()` loop
with a `Thread.sleep()` when we lose connection
* Clean up the `ImapMailReceiverTests` from `TaskScheduler` not used anymore.
* Expose new `taskExecutor` option in the `ImapIdleChannelAdapterSpec` for Java DSL
* Enable `ImapMailReceiverTests.testIdleWithMessageMapping()` with an attempt to see
if this fix covers an unclear problem exposed before
* * The `testIdleWithMessageMapping()` still fails on GH actions
e4c1851c07