PoW: Raise to five zeros logs displaying matched challenge

Due to the increase of the common difficulty level, it makes sense to increase the display of logs matched challenge to reduce amount of generated logs in order to reduce the size of the log files. This constant shouldn't to big otherwise small CPU smiths wont get the hint that their node is forging.

changed milestone to %1.9

added M-prover S-request review T-enhancement labels

review: OK thank @moul

merged

mentioned in commit 4efded83