* Fix 1.20.2+ clients disconnecting when updating boss bars
On 1.20.2, the Minecraft client started clearing boss bars after the login packet, which meant that the ProxyServer#showBossbar API would result in the player getting kicked if the boss bar they were previously shown was updated after switching servers.
Therefore, I have added BossBarManager which drops boss bar packets once the client enters the configure phase to ensure that they do not disconnect, and then re-adds the boss bar once the client enters the login phase.
This ensures that clients do not receive boss bar updates for boss bars that they don't exist and causing them to disconnect. I have also taken care to ensure that this logic only applies on 1.20.2 and up, as it is not necessary for older clients.
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Co-authored-by: Adrian Gonzales <adriangonzalesval@gmail.com>
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