Enable ZIP-215: Ed25519 Validation Rules

[dconnolly]

Solution

We need to upgrade our version of ed25519-zebra to use the validation rules in ZIP-215 and actually validate the Sprout Ed25519 signatures for full Sprout validation.

https://zips.z.cash/zip-0215

This involves pulling in the latest version of ed25519-zebra, checking that our async Verifier is well tested against the new rules, and making sure this validation is done by default on all blocks.

Alternatives

We could just use the new rules on blockheight >= Canopy, but that complicates our code.

[teor2345]

We can just use the new rules for all blocks (including pre-Canopy blocks), because the new rules allow all valid old signatures.