Spec "Goblin kernels"

[ledwards2225]

Idea here is to set a max op queue size and do client-side goblin recursion as necessary to avoid exceeding that limit. This would allow an unbounded "stack depth" while maintaining a fixed IPA MSM size (of our choosing).

Relatively simple conceptually but lots of design details to be considered, including:

• How exactly is a goblin kernel triggered? Presumably needs to be triggered upstream of bb
• Vanilla Ultra recursion? Efficient two circuit Bn254-Grumpkin recursion? Goblin HN?
• Additional handling of pairing points / IPA claim propagation