[Proposal] DPC and Ledger decoupling

[howardwu]

💥 Proposal

Current Design

We currently implement a DPC struct that takes Components as input.

• DPC implements DPCScheme<L: LedgerScheme>
• Components implements DPCComponents
• L: LedgerScheme is an associated item in all DPC instantiations

The result is that we must use DPC with DPC<Components> where L: LedgerScheme<{bind Components to LedgerScheme types}>.

Proposed Change

We decouple LedgerScheme from DPCScheme, so that an instantiated Ledger is independent. This allows us to merge DPCComponents associated items to DPCScheme, and move ledger-integrated methods in DPCScheme to LedgerScheme.

Finally, we can rename the current Components to DPC, and the current DPC to Ledger.

New Design

We implement a DPC struct that implements DPCScheme, which includes its associated types built in.

We implement a Ledger struct that implements LedgerScheme, which includes ledger-integrated methods in it.

[howardwu]

One of the major benefits to this architecture will be the ability to test DPC circuits without need for a fully-instantiated ledger as we currently do in .integration/.

[howardwu]

Discussed with @weikengchen offline, sounds like we are in agreement with the benefits of the change.

I will add this to the testnet2 checklist.