Refactor pickles to delay prev proof processing

[mrmr1993]

This PR does some refactoring of pickles, in particular to delay the processing of 'previous proofs' until the pickles circuit code has already started running.

This PR does not make the actual changes to allow passing the public inputs of the ancestor proofs from the main circuit; instead, this simply introduces mutable references and lazy computations to make it possible to do so. The changes to consume those public inputs and proofs from the circuit will be done in a follow-up PR.

This PR is part of a series, building upon #11008.

Note for reviewers: It will be easiest to review this PR commit-by-commit, and with whitespace changes turned off (there are some nesting changes that caused a lot of changes to indentation).

Checklist:

• Modified the current draft of release notes with details on what is completed or incomplete within this project
• Document code purpose, how to use it
  • Mention expected invariants, implicit constraints
• Tests were added for the new behavior
  • Document test purpose, significance of failures
  • Test names should reflect their purpose
• All tests pass (CI will check this if you didn't)
• Serialized types are in stable-versioned modules
• Does this close issues? List them

[imeckler]

Approved, sorry for the delay