make ProgramJson serializable

[tarrencev]

Resolves #1183

[Oppen]

I'm not 100% convinced this is the right solution. That said, I'm willing to merge something like this mostly because it's harmless for the most part. ProgramJson is out of the hot path so it's less likely to change and break the serialization format.

That said, we need tests for this, at the very least unit tests but preferably integration tests too to see how the feature is used, etc.

[kariy]

That said, we need tests for this, at the very least unit tests but preferably integration tests too to see how the feature is used, etc.

Not sure how to write a meaningful test for this, we only need it to convert Program into bytes, because we exclusively use it to marshal between contract types coming from different crates...

This is our use case for it:
https://github.com/dojoengine/dojo/blob/86f448c38cb21d7feb52d89cf48aea3b73648739/crates/katana/rpc/src/utils/contract.rs#L26

[Oppen]

Not sure how to write a meaningful test for this

I'd be happy enough with something with a logic like the following:

1. Write a JSON string that looks like what you expect.
2. Deserialize it into ProgramJson.
3. Serialize the result.
4. Deserialize again into ProgramJson.
5. Check both instances are equal.

The logic seems convoluted, but it'll save you from considering all the irrelevant differences that might come from formatting or field ordering if comparing the raw strings, while ensuring future changes remain compatible with that text representation.
Do note you can't rely on a hash of this data here to match between two different serializations, and that should probably be documented somewhere. That said, the team still needs to define a good policy regarding docs so I'm not gonna be pressing that yet.

we only need it to convert Program into bytes, because we exclusively use it to marshal between contract types coming from different crates...

All API surface needs to consider a bit more than the special cases that point out a need, as it always come with some maintenance baggage. I don't intend to be a PITA, I'm just trying to make sure we don't create problems for downstream users and collaborators (including you) in the future. Serialization format is part of that.

[Oppen]

Hey, sorry I didn't notice the new changes!
It looks ready to merge except for a last suggestion.

[Oppen]

Let's take a reference here. Since we're already cloning the contents there's no need to drop the old instance.

[pefontana]

This implementation is done here #1458
Thanks @tarrencev, for the contribution, we used your commits!