Feature request: map int64/uint64 to BigInt

[bin-y]

BigInt is a built-in object that provides a way to represent whole numbers larger than 253 - 1, which is the largest number JavaScript can reliably represent with the Number primitive and represented by the Number.MAX_SAFE_INTEGER constant. BigInt can be used for arbitrarily large integers.

Reference of BigInt here

[bin-y]

Sorry I didn't notice the doc about handling bigint with extensioncodec.
But I think it's kind of weird to do this with extension codec, as both int64 and uint64 are native types of msgpack.
I'm using nodejs to process python packed message. Solving the problem in this way I'll have to write an extensioncodec in python to encode int64. But the official python library supports encoding int64 to message with standardized format code which is more compatible when making cross-language systems.

[bin-y]

making a new issue as the problem is not well-described in this one