funding: skip rescan for already-confirmed zero-conf channels

[hxrshxz]

Change Description

Fixes #9299. On restart, zero-conf channels that are already confirmed no longer trigger historical chain rescans from the broadcast height, reducing bandwidth usage on mobile/neutrino.

Steps to Test

1. Open a zero-conf channel and wait for it to confirm
2. Restart lnd
3. Check logs - no rescan from broadcast height should occur

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the positive and negative (error paths) are included.
• Bug fixes contain tests triggering the bug to prevent regressions.

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• There is a change description in the release notes, or [skip ci] in the commit message for small changes.

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[gemini-code-assist]

Summary of Changes

Hello @hxrshxz, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces an optimization for how LND handles already-confirmed zero-confirmation channels upon restart. By intelligently using the confirmed block height as a starting point for chain rescans, it eliminates redundant data retrieval from the initial broadcast height. This change primarily benefits mobile and Neutrino users by reducing bandwidth usage and improving the overall performance and responsiveness of the client after a restart.

Highlights

• Optimized Chain Rescans: For already-confirmed zero-confirmation channels, the system now uses the confirmed block height as a hint for chain rescans instead of the initial broadcast height.
• Reduced Bandwidth Usage: This optimization significantly reduces the historical rescan range, which is particularly beneficial for mobile devices and Neutrino clients, leading to lower bandwidth consumption.
• Improved Restart Performance: Upon LND restart, confirmed zero-conf channels will no longer trigger unnecessary historical chain rescans, improving the startup efficiency.

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[gemini-code-assist]

Code Review

This pull request introduces an optimization to skip chain rescans for zero-conf channels that are already confirmed upon restart. This is achieved by using the confirmed block height as a hint for the chain notifier and by adding a check to skip the rescan logic if a zero-conf channel is already confirmed. The changes are logical and well-implemented. My main feedback is regarding the lack of tests to cover this new logic and prevent future regressions.

[gemini-code-assist]

While the logic to skip the rescan for already confirmed zero-conf channels is sound, this bug fix would benefit from an accompanying regression test. A test case could be added to simulate a restart where a zero-conf channel is already confirmed, and then assert that no historical rescan is triggered. This would help prevent future regressions and ensure the long-term stability of this optimization.

[yyforyongyu]

Thanks.

Why are we skipping the ci here?

[hxrshxz]

Thanks.

Why are we skipping the ci here?

Oops , mb I used copilot's "generate commit message" and didn't notice the skip ci , I will remove it from both the Title and the commit msg
thanks