feat: check existence of vk in contract tree

[iAmMichaelConnor]

Description

Note: added acir_hash to the PrivateCallData struct - this will need to be mirrored in the TypeScript struct.

Checklist:

• I have reviewed my diff in github, line by line.
• Every change is related to the PR description.
• I have linked this pull request to the issue(s) that it resolves.
• There are no unexpected formatting changes, superfluous debug logs, or commented-out code.
• There are no circuit changes, OR specifications in /specs have been updated.
• There are no circuit changes, OR a cryptographer has been assigned for review.
• I've updated any terraform that needs updating (e.g. environment variables) for deployment.
• The branch has been rebased against the head of its merge target.
• I'm happy for the PR to be merged at the reviewer's next convenience.
• New functions, classes, etc. have been documented according to the doxygen comment format. Classes and structs must have @brief describing the intended functionality.
• If existing code has been modified, such documentation has been added or updated.

Note
If you are updating the submodule, please make sure you do it in its own special PR and avoid making changes to the submodule as a part of other PRs.
To update a submodule, you can run the following commands:

$ git submodule update --recursive

Alternatively, you can select a particular commit in barretenberg/aztec3 that you wish to point to:

$ cd barretenberg
$ git pull origin aztec3        # This will point to the latest commit in `barretenberg/aztec3`
$ git checkout <commit_hash>    # Use this if you wish to point to a particular commit.
$ cd ..
$ git add . && git commit -m <commit_msg>
$ git push

[iAmMichaelConnor]

Looks good! Thanks for taking this over, and for the simple root_from_sibling_path function. Would be nice to refactor the bberg Merkle Tree code to a few simple functions one day.
(Github won't actually let me approve, because I authored it).