Implement Prop#324

This is the ticket for implementation work on congestion control algorithms: https://gitlab.torproject.org/tpo/core/torspec/-/blob/master/proposals/324-rtt-congestion-control.txt

Sub-tickets:

• Handshake negotiation spec: #40377 (closed)
• Flow Control implementation: #40450 (closed)
• Full negotiation implementation: #40444 (closed)
• Parameter default update and other fixups from simulation: #40524 (closed)
• Unit testing work: #40443 (closed)
• Simulation work: #40404 (closed)
• Flow control XON/XOFF pseudocode specification: #40573 (closed)
• Specification updates: #40572
• Extra-info fields for flow control: #40477 (closed)