Fix more issues with despawning

[DrakiaXYZ]

• Don't despawn any bots that haven't been alive for atleast 10 seconds (Stops issues with despawning a bot directly after it spawns)
• Perf optimization: Don't use LINQ (memory allocation), and use .sqrMagnitude instead of Vector3.distance (avoid square root)
• Remove bot from bleeding character list before despawning
• Switch to new despawn method that doesn't utilize asset pool, to avoid issues we had with gameObject re-use