Check chain watcher for combined reports

[Kivou-2000607]

Marvin: <@!610536996485726209>
You can report your bug here.

savit [1899598]: Chain watcher calculation seems to be off for combined chains

savit [1899598]: it seems to be averaging the chain watcher uniformly over all chosen chains, rather than weighting by length of chain

savit [1899598]: This person only contributed in the last chain chain of 31, and not in 250, and yet have much higher chainwatcher than they should , since the averaging is uniform weights

Kivou [2000607]: mmm right, for this I'll have to take a deep look. It possible that I omitted this details.