Floodgate: Report observed TPS every 60s

Fancy log to have a sense of what is happening.

Mar 07 16:59:06.327: measured 1.81664 transactions per second over the past 1min

Manually testing the MR

./floodgate run --controller 0x3a6a6ca30c1ef1ce605a63a7a1a4ff4c689f8414ca0838bca29423f0ec280ff5 --tick-interval 0.5 -m 1