Cancel unused timers when completing the state for optimization

This will save some workflow tasks completion events for Cadence/Temporal

see https://github.com/indeedeng/iwf/discussions/321

Start with discussion #321 to understand the proposed optimization and its expected behavior. No files or tests are named in the issue; trace state-completion and timer handling in the repository, then verify that unused timers are cancelled and fewer Cadence/Temporal workflow-task completion events are produced.

Written by the indexing model from the issue text.