update protocol packet definitions: replace value receivers with pointer receivers in PacketID methods, expand FixedBitSet size from 8 to 256 bits, and remove outdated documentation files

pkg/protocol/packet/game/server/keep_alive.go

@@ -7,7 +7,7 @@ type KeepAlive struct {
 	ID int64
 }
 
-func (KeepAlive) PacketID() packetid.ServerboundPacketID {
+func (*KeepAlive) PacketID() packetid.ServerboundPacketID {
 	return packetid.ServerboundKeepAlive
 }