Incorrect exit_time in PositionExit event during backtesting

[ahmedxfn]

When listening to engine events during backtesting, I've encountered an issue where the PositionNew event correctly reports the entry time. However, for the PositionExit event, the exit_time field is always set to the current time instead of the actual exit time from the past.

Expected Behavior:

The exit_time in the PositionExit event should reflect the exact time when the position was exited, as recorded in the backtest, rather than the current time.

[just-a-stream]

Hey @ahmedxfn, thanks for opening this. It's a valid point.

I've re-written the whole of barter now so there is a new trait EngineClock that begins to handle this "backtest time" problem via it's HistoricalClock implementation.