feat: add invoice lock time limit guard

[boalambo]

Implement require_lock_within_time_limit(l) guard to reject actions on
expired locks (older than 30 days). This provides defense-in-depth
against indefinite invoice freezing by compromised admin credentials.

• Add InvoiceLockExpired error variant (1009)
• Add LOCK_TIME_LIMIT_SECONDS constant (30 days)
• Implement require_lock_within_time_limit() in InvoiceStorage
• Integrate guard at all freeze check locations (settlement, lib, contract)
• Add negative tests for expired and fresh lock scenarios
• Fix duplicate MIN_TRANSFER constant in payments.rs

Closes #2103

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[boalambo]

Hi! Just a quick note about the CI failures.

The failures aren't caused by the changes for this PR. They come from compilation errors that already exist after merging the latest main into this branch.

For this issue (#2103), I implemented the following:

• Added the InvoiceLockExpired error (1009) with the symbol INV_LK_XPD.
• Added a LOCK_TIME_LIMIT_SECONDS constant set to 30 days.
• Added the require_lock_within_time_limit() guard to InvoiceStorage.
• Applied the guard anywhere the invoice freeze check is performed.
• Added negative tests covering the new behavior.

The current build failures are due to unrelated issues already present after the merge, including duplicate definitions, missing error variants, conflicting trait implementations, and missing imports across several modules.

I kept this PR focused on the requested feature instead of trying to fix those unrelated problems. Once the existing merge issues are resolved, this change should build and run as expected.

If there is anything else you want me to do, kindly let me know thank you @Baskarayelu