Function: witness_at_epoch
This is the main entry point for witnessers to acknowledge a call on chain in the multi-sig.
Votes are stored in the Votes pallet storage at a specific index for each voter. A voter can only vote once, and once the threshold of voters has been reached, the call is either made using the dispatch_call function or the call is scheduled in WitnessCallsScheduledForDispatch if the SafeMode pallet specifies not to dispatch the call.
If the epoch_index of the witnessed call is less than or equal to the last expired epoch, the witnessed call does not execute. The following code also constrains epoch_index to ensure it is less than or equal to the current epoch index:
Scheduled calls are executed in the on_idle if sufficient weight remains at the end of each block and SafeMode permits it.