Ensure sessions are removed when a transfer packet is sent or they exit without the form

[Konicai]

• Removes usage of GeyserSession from the storage and server managers, instead using Connection api
• Don't allow GC to start on Geyser instances with auth-type: offline since it breaks GeyserConnect and doesn't have any affect on what kind of servers you can connect to.
• Restore the original packet handler when a transfer packet is sent to reduce likelihood of breakages
• Ensure session disconnect occurs when onDisconnect is called on the GC custom PacketHandler, by also calling the original packet handler
• The previous two points combined will ensure that the session is removed when it wasn't previously:
  • A transfer packet is sent to them
  • They leave GC by force closing the client
  • They leave GC by spamming the escape key to access the client settings and leaving from there

This does not fix the issue where two clients can join with the same account, which should probably be added as an additional check within Geyser.

I have tested this on my local testing instance, transferring to the geyser test server, and also joining it as a java player using GC. Would appreciate if someone could also do some as a double check because I really don't want to accidentally break the public GC :)