ADVZ PayloadProver intelligently use Small or Large range proof

[ggutoski]

Based on Originally posted by @ggutoski in #438 (comment)

Problem

SmallRangeProof is strictly worse than LargeRangeProof if the given range is large. We should make it easy for the user to avoid misuse of SmallRangeProof.

Proposed solution

Add another impl of PayloadProver that intelligently selects the proof type based on the user's input. The return type would be an enum with Small and Large variants. The existing impls for Small and Large remain as-is so that the user retains the ability to enforce a preference for Small or Large.