Rework resuming

[freyacodes]

This PR includes the following changes:

• Adds caching of the Session entity, used by the disconnect code
• If resuming is configured on the server, the client will wait with moving the links to a different node until the first unsuccessful connection attempt
• If a connection is successfully resumed, the client will refresh the player and link state
• Added the new ResumeSynchronizationEvent event after refreshing remote state after a resume
• Added LavalinkNode#getCachedPlayers()
• Potentially breaking: ClientEvent is no longer sealed

Not tested since 8edae46

[duncte123]

Looks good. If we really wanted we could add that get endpoint for the session and push a major version of this client that only supports that new version of the server. That would also remove the possible breaking concern of the non sealed class

[freyacodes]

This seems to be working consistently now