RHGitaly ListLastCommitsForTree

Everything is in place for oxidation of this one, as the core logic is the same as in LastCommitForPath.

It is currently one of the most frequently called HGitaly methods, and is very slow. Here is an excerpt of foss.h.n statistics about the last 8 hours:

hgitaly-stats log/hgitaly.log --since 2024-07-08T01:29:26.589849 | head
TOTAL Requests since 2024-07-08 01:29:28,826: 6254 
      239 incomplete (cancelled or failed)
Breakdown:
  38.0% FindCommits (called=2392, incomplete=121, average_time=502.8ms, worst_decile=861.6ms)
  13.0% ListLastCommitsForTree (called=830, incomplete=0, average_time=2554.3ms, worst_decile=6354.9ms)

hence can induce worker starvation. Also has a great impact on user experience (browsing repositories, including projects default home page)