Support Gilbert-Elliott packet-loss model

Replace LinkConditioner's per-packet drop rate with a two-state
Gilbert-Elliott Markov model so simulated packet loss occurs in
correlated bursts, matching real packet-loss behavior.

Give `LinkConditioner` a good/bad state. A good state denotes the link
is healthy and not dropping packets. A bad state denotes the link is
dropping a lot of packets. It also opens up the possibility of adding an
extra latency to packets during a bad state.

Add builder methods to `LinkConditionerConfig` to configure the packet
loss model.

Closes #1546.

Author: nick-e

crates/io/link/Cargo.toml

@@ -28,6 +28,9 @@ bevy_ecs.workspace = true
 bevy_reflect.workspace = true
 bevy_utils.workspace = true
 
+[dev-dependencies]
+approx.workspace = true
+
 [lints]
 workspace = true