Fix idempotent send with delay

[slinkydeveloper]

Fix #1678

This PR essentially reorganizes the code around handling the folllowing events in the state machine:

• Handle the Command::invoke. Now everything is under handle_service_invocation. Of the changes within this code, the important ones are:
  • I moved the deduplication of workflow calls before the scheduled invocation check
  • I now handle the case of SourceTable::New for the scheduled calls
  • Fix the case of send with execution delay only responds with invocation id after delay #1678
• Handle the new Timer::NeoInvoke

This also includes:

• Reorganize a bit the code around the inbox handling to unify with the above code
• Add several tests, including one for the inbox

There's also a bit of reorganization of the NeoInvocationStatus materialized type, to share the common values of Inboxed/Scheduled in a single data structure.

[slinkydeveloper]

Related to this #1844

[tillrohrmann]

Great work @slinkydeveloper. The on_service_invocation is structured in a way that makes it a lot easier to understand what's going on. Well done. LGTM. +1 for merging if GHA gives green light.