Rollback Example

[Giesch]

This adds a rollback netcode example based on the Guilty Gear Strive pseudocode docs here. This version is reliant on TCP for message ordering and handling packet loss; we can modify it to use an unreliable socket in the future. This now uses an unreliable channel and tries to account for missing or out-of-order input messages, but I haven't properly tested it with remote players.

Remaining work:

• resolve in-code todo re: tickOnce
• use a non-empty list or ringbuffer type for inputs
• docs
• fix roc_panic message handling
• duplicate recent messages each frame
• handle out-of-order messages
• message instead of crash on desync
• switch to unreliable channel, mitigate packet loss
• test more, discover more bugs
  • address __checkstk_ms windows linking bug