Rewrite congestion and recovery code

This is a significant change that replaces most of the congestion
and recovery control implementation with an implementation that
mostly ports the one from google/quiche. IMHO The change nicely
breaks up congestion, recovery and pacing into separate, easily
mainatinable and extensible pieces, and is also more idiomatic.
The advantage of porting from google/quiche is that at least
the cubic and pacing codes are very well tested, and require
minimal review. The new pacing implementaion is also more accurate.

apps/src/bin/quiche-server.rs

@@ -537,6 +537,7 @@ fn main() {
                 client.loss_rate = loss_rate;
             }
 
+            #[allow(deprecated)]
             let max_send_burst =
                 client.conn.send_quantum().min(client.max_send_burst) /
                     client.max_datagram_size *

quiche/Cargo.toml

@@ -66,6 +66,7 @@ foreign-types-shared = { version = "0.3.0", optional = true }
 qlog = { version = "0.9", path = "../qlog", optional = true }
 sfv = { version = "0.9", optional = true }
 smallvec = { version = "1.10", features = ["serde", "union"] }
+enum_dispatch = "0.3"
 
 [target."cfg(windows)".dependencies]
 winapi = { version = "0.3", features = ["wincrypt", "ws2def", "ws2ipdef", "ws2tcpip"] }