Use unmined types for transaction verifier mempool requests and responses

[teor2345]

Motivation

Now that zebra-network uses unmined types for transactions, we also need to use them in the transaction verifier's Mempool request.

Solution

• Use UnminedTx in transaction verifier Mempool requests
• Use UnminedTxId as the transaction verifier response type

We'll want the full witnessed ID even for Block requests, because it will help us diagnose mined transaction verification failures, and auth data root verification failures.

Minor cleanup:

• Refactor is_mempool into a transaction verifier request method
• Improve debug and trace logs

Review

@conradoplg might want this PR before starting work on #2637, so the types match up.

This PR is based on PR #2665, feel free to rebase it on main if needed.

Reviewer Checklist

• Code implements Specs and Designs
• Existing tests pass

We'll add more tests for this code as part of the mempool work.

[conradoplg]

Looks good! I've rebased and force-pushed after #2665 was merged, so I'll leave it for @teor2345 or @dconnolly to check if I did that correctly and merge this (and address @daira's comments if desired)