Allocations count is often an interesting proxy for performance,
but not necessarily the most relevant thing to include in request
logs, given they aren't a per thread metric, so the reporting
is widely innacurate in multi-threaded environments.

Since Ruby 3.1 there is now `GC.total_time` which is a monotonically
increasing counter of time spent in GC. It still isn't really a per
thread metric, but is is more interesting because it uses the same
unit as the response time, allowing to better see when you have a GC
pause performance issue.