Tune KIST and EWMA with Congestion Control

Once congestion control (Proposal 324) is implemented, we will need to re-visit our KIST and EWMA parameter choices and performance, as EWMA will provide better fairness properties by increasing RTT of overly loud circuits, which will cause congestion control to back off.

The KIST interval will also influence the number of circuits that can be involved in prioritization decisions. Larger intervals mean lower throughput, but more prioritization choice. Smaller intervals mean higher throughput, but less prioritization choice.

For some additional background on KIST tuning, see #29427 (closed).