build(deps): Bump zcash_client_backend from 0.10.0 to 0.12.1

[upbqdn]

Motivation

Close #8541.

PR Author Checklist

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• Will the PR name make sense to users?
• Does the PR have a priority label?
• Have you added or updated tests?
• Is the documentation up to date?

Solution

This PR is currently only a draft and doesn't compile.

• Bump zcash_client_backend from 0.10.0 to 0.12.1.
• Fix breaking API changes.

Reviewer Checklist

Check before approving the PR:

• Does the PR scope match the ticket?
• Are there enough tests to make sure it works? Do the tests cover the PR motivation?
• Are all the PR blockers dealt with?
  PR blockers can be dealt with in new tickets or PRs.

And check the PR Author checklist is complete.

[oxarbitrage]

Replaced by #8568