The extra buffer used to decode the strings sent by the client
in the legacy ping protocol was never released. However, creating
an extra copy of the buffer just to decode it to a string isn't
actually necessary: We can just call toString() directly on the
original buffer.
Additionally, free the buffer in handlerRemoved() to handle cases
where the client never sends enough bytes to form a valid legacy
ping request.
This enables us a fast reference to the entities current chunk instead
of having to look it up by hashmap lookups.
We also store counts by type to further enable other performance optimizations in later patches.
