[Feature]: Unify sBTC testnet tokens

[djordon]

Feature - Unify sBTC testnet tokens

1. Description

There are two main sBTC tokens on testnet: one we deployed as part of our testnet signer deployment, and one deployment managed by Hiro. That's unfortunate on its own, but it's even stranger since:

1. Clarinet links to Hiro’s token,
2. The Explorer links to our token, and
3. Leather recognizes our token as sBTC, and marks Hiro’s token as suspicious.

I'd like us to consolidate on our sBTC testnet token. We want to maintain a proper testnet signer deployment anyway, and it seems strange to have a canonical testnet sBTC that we don't manage. However, this means ensuring developers can easily access testnet sBTC. The problem is that acquiring our testnet sBTC requires you to first acquire testnet BTC and then bridge that into sBTC. We probably want an experience that is similar to what Hiro provides where you click a button and testnet sBTC magically appears in your wallet.

2. Technical Details

One way to make sure that we have a simple developer experience on testnet is the following:

1. Have a script that requests BTC to some address as a cron job. This address will be an sBTC deposit address.
2. Use spox to watch for that address and inform Emily when it sees the UTXOs confirmed on testnet.
3. Some wallet would then receive sBTC regularly, so it could send some to people on request. Hand out this sBTC using the same Hiro UI, but from a wallet that is refilled using the above process.

This way, we would be pretty confident that developers who need testnet sBTC can get as much as they like, and we would always be using our infrastructure/applications so it would serve as a good testbed for any changes before a mainnet release.

2.1 Acceptance Criteria

• There is only one main sBTC on testnet
• The process where developers acquire sBTC on testnet is just as simple as it is now.

3. Related Issues and Pull Requests (optional)