Zsa1 diff, for reference only

[PaulLaux]

This PR implements draft ZIP 226 and draft ZIP 227

What's included:

• Issuance: Issuance PR:
• Burning mechanism: the ability to publicly burn ZSA notes. This is done by adding a burn field inside the Orchard bundle and the ability utilize it. In addition the changes to bvk and bsk to support this change. See ZSA burn functionality #35 for full list of changes.

/// A bundle of actions to be applied to the ledger.
#[derive(Clone)]
pub struct Bundle<T: Authorization, V> {
    /// The list of actions that make up this bundle.
    actions: NonEmpty<Action<T::SpendAuth>>,
    /// Orchard-specific transaction-level flags for this bundle.
    flags: Flags,
    /// The net value moved out of the Orchard shielded pool.
    /// This is the sum of Orchard spends minus the sum of Orchard outputs.
    value_balance: V,
    /// Assets intended for burning
    burn: Vec<(AssetId, V)>,
    /// The root of the Orchard commitment tree that this bundle commits to.
    anchor: Anchor,
    /// The authorization for this bundle.
    authorization: T,
}

• Note Encryption: We extended the Domain trait in the zcash_note_encryption crate to support various lengths for COMPACT_NOTE_SIZE by converting the relevant constants into trait specific types. Later, implemented OrchardDomainV3 to support the new note structure. See the supporting PR for more details: zcash_note_encryption generalization zcash/librustzcash#746 and V3 encryption #38
• Updated the Python implementation to support the changes. See: Testing encryption v3 zcash-test-vectors#6 and the zsa1 branch for full details.
• Test vectors for AssetID derivation AssetID test vectors #34
• Split note mechanism.
• Circuit changes to support AssetID, split notes, and all other new functionality.
• Backward compatibility with Orchard bundles.

The proposed changes should be considered as a Draft and should not be considered as final.