Release LSPS2 intercepted HTLCs on open failure

[tnull]

When a JIT channel open fails, release queued intercepted HTLCs through the intercept API so they are not held until expiry. Keep resetting the LSPS2 state if an intercept has already been released.

Co-Authored-By: HAL 9000

This finding was discovered by Project Loupe

[ldk-reviews-bot]

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[ldk-claude-review-bot]

No issues found.

The change correctly fixes a real bug: fail_htlc_backwards_with_reason(payment_hash, ...) operates on claimable payments and is a no-op for intercepted HTLCs (which live in pending_intercepted_htlcs), so previously the queued HTLCs were never released and stayed held until expiry. Replacing it with fail_intercepted_htlc(htlc.intercept_id) is the correct API and is consistent with the existing pattern at service.rs:1050.

Verified:

• InterceptedHTLC.intercept_id exists and is the right identifier.
• Swallowing the result with let _ = is intentional and safe — in PendingChannelOpen state the only expected error is "not found" (already released), matching the PR description.
• The removed FailureCode import has no remaining uses in the file.
• No new lock-ordering/deadlock risk (peer_state → channel_manager ordering unchanged from the old code).
• The new test genuinely registers an intercept via the real payment flow and asserts it is released after channel_open_failed.

[ldk-reviews-bot]

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[TheBlueMatt]

Backported in #4683.