feat: add merkle tree test suite

[wolfv]

Summary

Release Note

Documentation

[wolfv]

Looks like the upstream tests are also passing in this branch! :)

I also made the PR to @vembacher repository. I did have to merge main and get rid of a few merge conflicts, which is why the PR looks a bit messy: vembacher#1

I'll tackle the remaining cargo hack issues.

[wolfv]

Thanks @flavio for merging serde_json_canonicalizer! Merged main again, and moved everything over from olpc-cjson.

[viccuad]

Hi, thanks for tackling this.

Sadly, I cannot humanly review a merge commit with 89 changed files nor I can blindly trust it. Hence I elected to perform it on my own plus minimal fixes on #285.

Can you rebase or cherry pick 484468e on top of the current state of #285 please?

In addition, that commit will not pass make test locally. For that, I would like the merkle tests to be gated under a feature, and a new make target to run them. For now we can keep obtaining the testcase files as a manual step; I would like to keep it simple without submodules, nor importing the history of transparency-dev/merkle, nor copy-pasting them and needing to diff between the repos every time they are updated.

[wolfv]

I'm happy to make a new PR with the test suite after vembachers pr is merged. This was mostly a demonstration that tests pass.