Adds int64 optional format test

[spacether]

Adds int64 optional format test, an openapi numeric format

[Julian]

Cool! Though sorry if I was unclear in the slack message -- by "help bootstrap" what I meant was -- I do think we should have these kinds of tests because they're useful to implementers of JSON Schema tooling, but I'm not convinced we should have them here precisely in this repo. I think we should have them in a parallel one which would have as its scope "all the formats in the OpenAPI format repository".

But yeah, I'm hesitant to add anything to this repository that isn't really part of JSON Schema "the specification itself".

I'm happy to create a parallel repository in the org we could use for that purpose -- and/or we can see whether others have opinions, but it doesn't feel totally right to have these here at first glance.

[spacether]

Reading the json schema spec, it allows custom formats and these custom formats have been in the openapi spec and the wild for years. Why not allow it here as an optional custom format?

[Julian]

Because doing so can easily be confused with "officially endorsing" a particular version or set of formats, and there isn't such endorsement from the JSON Schema spec or team. If there were, it'd be much easier to consider including them here.

There's already enough confusion about what the various files in the optional directory mean (see e.g. #590 which is trying to fix that)

[spacether]

Understood; another repo it is. Not sure where that repo should live though.
Maybe in https://github.com/OAI?
@MikeRalphson @earth2marsh @whitlockjc @webron @handrews what do you think?