feature: add conditional support for serde

[hackaugusto]

Describe your changes

Adds conditional support to serde. This can be used to serialize the data as JSON to encode the mock chain data.

This depends on facebook/winterfell#209

Checklist before requesting a review

• Repo forked and branch created from next according to naming convention.
• Commit messages and codestyle follow conventions.
• Relevant issues are linked in the PR description.
• Tests added for new functionality.
• Documentation/comments updated according to changes.

[frisitano]

Left a suggestion inline. Let me know what you think.

[hackaugusto]

some notes:

• I have updated the code to emit a hex encoding for the rpo and blake digests
• I assumed this should not have additional libraries, so instead of using the hex dependency there is some simple code to do the serde of the types
• I made the prefix 0x required for simplicity, this can easily be lifted if necessary

I now have to look how to skip encoding the inner nodes of the trees / merkle store

edit: for the time being we are serializing the whole structures, if it becomes a necessity skipping the inner nodes can be implemented

[bobbinth]

Looks good! Thank you! I left question/comment inline - if you agree, we can implement these checks and merge.

[frisitano]

Looks good! Would be good if we can leverage the hex utilities you have introduced for midne-vm as currently have a bit of logic duplication.

[frisitano]

We have a similar utility downstream in miden-vm. Would be good if we can purge that and leverage this. https://github.com/0xPolygonMiden/miden-vm/blob/105ee9e241fafeac97fbcd14861b2eaed5548e1e/assembly/src/ast/parsers/labels.rs#L77-L93