Cap CLI stdin concat in msgpack2json / json2msgpack

[enochgroot]

bin/msgpack2json and bin/json2msgpack push stdin chunks then Buffer.concat with no ceiling, then unpack / JSON.parse.

Cap accumulated stdin bytes before concat/parse. Fail closed with a documented limit.

[enochgroot]

Implemented in #14 (branch fix/review-open-6-13).

[enochgroot]

Tracked upstream: msgpack#25701

Closing this fork issue as a duplicate of that ticket. Numbering on enochgroot/msgpack-node is a different sequence from msgpack/msgpack-node.