Enhancement

Cache username-uuid mappings on the server side when a player enters the server, and request the server side cache if the client is unable to get the pet owner's name.
This feature allows the pet owner lookup to work even if the client is not in stable communication with the Mojang server or if the server has online mode disabled (only if the mod is installed on the server).
This is also helpful for servers that have the fake player feature enabled (e.g. Carpet Mod), as it may not always be possible to get the name of the fake player.