Create a ZIP draft for a ZIP on Regtest mode on Zcash Full Nodes implementations.

It should describe at least the current state of Regtest on Zcashd so that it can be implemented on Zebra.

After Zcash deprecation new features shall be added to Regtest definition. At this very moment (Feb 2025) we just need Parity between Zcashd and Zebra for development purposes.