Improve zigzag example

[porcuquine]

Description

The zigzag example needs some improvements as part of a push to reconcile security and scaling requirements.

Non-exhaustively:

• Support tapered challenges
• Use less memory so larger parameters can be generated
• Log individual partition proof timing
• Update defaults
• Don't hold onto data during proof generation. Current implementation does so in case of extraction, but we don't really use that. Consider removing.
• Don't duplicate vanilla proving (it's included in CompoundProof generation). If we had a better way of gather granular timing/profiling of internal parts, we could use that. We should. Meanwhile, now that vanilla proving is fast, it's not a huge deal — but for correctness it should not be added to total proving time.

Acceptance criteria

Risks + pitfalls

Where to begin

[dignifiedquire]

Zigzag examples is moving into filbase, closing this issue for now. Will track new requirements there