Log recognition time duration and warn if it is abnormal

[denis-stepanov]

Currently we have -l debug producing something like this:

2024-05-23 00:22:59,659 Thread-1 DEBUG: Recognition start=00:22:53,936, end=00:22:59,659, match FR_TF1SERIESFILMS_220824_EVENING1_3, 0% confidence

The "end" time is hard to interpret (one has to subtract); it would be better to print duration (= end - start) instead.

Also, AdVent engine assumes that recognition runs for no longer than i + REC_DEADBAND time, where i is recognition interval parameter and REC_DEADBAND is a hardcoded constant (before issue #24 is resolved). So it would be good to report if de-facto recognition duration exceeds forecast by a good margin (say, by more than 0.5 s), as it could affect AdVent efficiency.