Optimise tracking of deferred timings in DelegatingRateLimiterImpl request-release timing #555
Description
As of #552, the DelegatingRateLimiter implementation buffers request-release timings from its inner rate limiter.
Today it uses a sorted std::list to accomplish this, but there are probably more efficient means to pull
this off when there are many timings to track.
Context: 131d2e0#r495628578