refactor: add nonce tracking in TaskResult to index app.signer txns

[fubuloubu]

What I did

Added nonce tracking logic into SilverbackMiddleware, which updates a label in .post_execute that gets stored in TaskResult. If you know the account address, you can do additional parsing post-task (assuming that the transaction has been finalized) to obtain the transaction receipt information from this combination.

fixes: #88
fixes SBK-463

How I did it

Realized that SilverbackSettings was already passing itself to SIlverbackMiddleware

How to verify it

I ran the example app with --account <My wallet> and then separately sent a transaction from that wallet address in ape console

In production, it will be strongly suggested to never mix keys like this as it is not a good idea anyways (due to requirement for stateful nonce tracking), but it will also give you a false positive of what transactions occured in the task.

Checklist

• Passes all linting checks (pre-commit and CI jobs)
• New test cases have been added and are passing
• Documentation has been updated
• PR title follows Conventional Commit standard (will be automatically included in the changelog)

[linear]

SBK-463 Track `app.signer` transactions in `TaskResult`