Feature request: estimate merge time based on last merge

[paraw]

Often, the merge time of some packages differs massively between versions. For example, on one of my machines, it took 9 minutes and 30 seconds to merge llvm-3 and 32 minutes to merge llvm-14. I think it would be useful to compute the merge time of packages using the last logged merge time as an estimate, rather than averaging all logged merge times. Possibly, one could have a flag to switch between the two behaviours.