[Feature]: Handle requests that do not have a response exactly once

[djordon]

Feature - Handle requests that do not have a response exactly once

1. Description

When we reach out to the Emily API for deposit requests, we end up adding it to our list of deposits-to-watch-for each time. And every time there is a new bitcoin block we attempt to process "pending" deposits but our queries do not distinguish between deposits that do or do not have a response. This causes us to continually include deposit UTXOs in our bitcoin transactions.

1.1 Context & Purpose

When we get a request from Emily, make sure that it is added to our list of deposits-to-watch-for at most once. Update our queries to exclude deposit requests that have a response transaction that has been confirmed.

2. Technical Details:

2.1 Acceptance Criteria:

• The signers' deposits-to-watch-for list never contains duplicates.
• The signers never construct a response transaction for a deposit request if they have responded already and it is confirmed on the canonical bitcoin blockchain.
• We attempt to vote on a deposit or withdrawal request once.

3. Related Issues and Pull Requests (optional):