fix(test): Fixes a bug in the sending_transactions_using_lightwalletd test

[arya2]

Motivation

This PR fixes a bug in the sending_transactions_using_lightwalletd test where transactions from multiple future blocks are being sent to the mempool without committing prior blocks to the chain.

Solution

Submits blocks to the state after sending their transactions to the mempool.

Tests

The test should pass in CI.

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.

[arya2]

This test could also fail due to transactions having unpaid actions (which are allowed by default in blocks but rejected by default in the mempool).

I'm looking into why it failed here: https://github.com/ZcashFoundation/zebra/actions/runs/11979091682/job/33400891720?pr=9052#step:15:844 where that transaction did pay the conventional fee.

The log also indicates that lightwalletd can't parse errors returned from Zebra's sendrawtransaction method, seemingly because it's expecting a colon-separated string but is receiving JSON.