Introduce `CommitTxBlockHeight` field to the `ResolutionReq` structure
and related methods. This field records the block height where a
commitment transaction has confirmed.
This commit introduces a new `IsRunning()` method to the `StateMachine`.
This method allows callers to safely query whether the state machine
is currently active after it has been started and before it has been
stopped.
To ensure thread-safety, the internal `running` status flag is
implemented using `atomic.Bool` (from `sync/atomic`). Without atomic
operations, concurrent accesses to a simple boolean flag from different
goroutines (e.g., one goroutine calling `IsRunning()` while another
executes `Start()` or `Stop()`) could lead to stale reads or data races.
Ensure shutdown assertions through log inspection are only performed
when the harness node has an active log file handle. This avoids
errors during shutdown when log file output is disabled.
ffranr