research: Explore using zebra on disk database as a source of data for `zcash_client_backend`

[oxarbitrage]

An alternative to https://github.com/ZcashFoundation/zebra/issues/8358 will be to make the zcash_client_backend to read and use the data in the Zebra on disk database. A replacement of this kind will make all functionality of the crate to remain working as it is but pulling the data from that source instead.

[mpguerra]

@upbqdn do you want to do anything else here?

[upbqdn]

Yes, I would like to look into this.

[upbqdn]

The conclusion is that we can read the state similarly to how we're going to do it in the scanner.