Implement the jlap format

[wolfv]

It would be nice to implement the jlap format for partial repodata updates (using a specific sequenece of JSON patch applications).

That makes interactive usage faster because only a subset of the entire data needs to be fetched over the network.

[dholth]

This is the predecessor to the jlap forma in rust https://github.com/dholth/jdiff/. It is basically the same except that there is an array of patches instead of a line-based format.

It turns out Python has very fast json support (generating the patches on pypi was faster), and this was put aside.

[travishathaway]

@wolfv, please assign me to this issue.

@dholth, I would be happy to get your assistance on this if you're interested too.

[wolfv]

Just for reference, this was the prototype I made in C++: https://github.com/mamba-org/mamba/pull/2029/files