Move Utxo type to zebra-chain

[oxarbitrage]

Motivation

In the value pools design we created several methods that receive a Hashmap with Utxos, just as:

• https://github.com/ZcashFoundation/zebra/blob/main/book/src/dev/rfcs/0012-value-pools.md#create-a-method-in-input-that-returns-valuebalancenegativeallowed
• https://github.com/ZcashFoundation/zebra/blob/main/book/src/dev/rfcs/0012-value-pools.md#create-the-transaction-method
• https://github.com/ZcashFoundation/zebra/blob/main/book/src/dev/rfcs/0012-value-pools.md#create-a-method-in-block-that-returns-valuebalancenegativeallowed-for-the-block

However, the Utxo is a zebra-state type.

Note: zebra-chain do not depend on zebra-state

Designs

Value Pools Design

Solution

Move the state Utxo type into zebra-chain::transparent so we can have it available in method signatures. This is a pretty noisy change so i separated it from the value pool implementation but it is part of #1895

Review

I am not sure if we have a better alternative but i think this is needed. Anyone can review the code.

Reviewer Checklist

• Current tests pass all.

Follow Up Work

Continue the implementation of value pools in #1895

[teor2345]

I think this change is low-risk - we have existing Utxo tests, and the Rust compiler checks imports.

Thanks for splitting it out into a separate PR!

There are alternatives, but they make the code less readable and harder to test. For example, we could:

• impl extra methods on Block in zebra_state - but then those methods aren't available unless a crate depends on zebra_state
• add the method in zebra_chain, and make it generic over a trait - but that duplicates the method signatures

[teor2345]

I'm going to merge this now, because splitting #2420 also depends on UTXOs.