- UpdateNOC did not clear session of previous fabric like spec intended
  (project-chip#20379)
- All OpCreds cluster slow commands did not try to early-ack to avoid
  MRP timeouts (project-chip#19132)

Fixes project-chip#20379
Fixes project-chip#19132

This PR:

- Fixes UpdateNOC expiring all sessions for the updated node
- Adds `FlushAcksRightAwayOnSlowCommand` to CommandHandler to flush acks
  on slow commands
- Adds Python tests for UpdateNOC behavior of session expiring
- Adds `ExpireSessions` to Python for testing

Testing done:

- Unit tests all pass
- Cert tests pass
- With the session clearing, previous Python tests failed, until
  I fixed them with the new `ExpireSessions` API
- Observed standalone acks immediately sent on opcreds cluster commands