Fixes #24813: More change to prepare scala 3 migration

[fanf]

https://issues.rudder.io/issues/24813

See #5548 for the original PR.
I didn't saw anything strange, test pass, rudder seems to work.
Some commit warrant a second sight:

• provide a total function for messageHandler to avoid pattern matching catchall for future values
  c5098e0
• (*) rewrite early return function to functional style 613dcfe

That's all, other seems quite automatic / not risky.

[fanf]

Merging that PR. Everything seems OK, tests pass, rudder works.

[Normation-Quality-Assistant]

This PR is not mergeable to upper versions.
Since it is "Ready for merge" you must merge it by yourself using the following command:
rudder-dev merge https://github.com/Normation/rudder/pull/5639
-- Your faithful QA
Kant merge: "In law a man is guilty when he violates the rights of others. In ethics he is guilty if he only thinks of doing so."
(https://ci.normation.com/jenkins/job/merge-accepted-pr/83921/console)

[fanf]

OK, merging this PR