BOLT11 invoice follows the new spec changes

[MPins]

Fixes #9700 Fixes #9842

This PR updates the BOLT 11 invoice implementation to follow the new specification changes.

Specifically, it enforces validation of mandatory fields (p, h, s, n) and their expected lengths (52, 52, 52, 53 respectively).

[gemini-code-assist[bot]]

Summary of Changes

Hello @MPins, I'm Gemini Code Assist[^1]! 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 significantly enhances the robustness and compliance of BOLT 11 invoice handling by integrating the latest specification updates. The primary focus is on enforcing strict validation for critical invoice fields, ensuring that payment hashes, payment secrets, and destination public keys meet their specified length requirements. This change prevents the processing of malformed invoices, improving overall network reliability and security.

Highlights

• BOLT 11 Specification Compliance: The invoice implementation now strictly adheres to the latest BOLT 11 specification changes, ensuring greater interoperability and correctness.
• Mandatory Field Validation: Enforces validation for mandatory fields ('p', 'h', 's', 'n') to ensure they have their expected base32 lengths (52, 52, 52, 53 respectively).
• Stricter Error Handling: Instead of silently skipping fields with incorrect lengths, the system now explicitly returns an 'ErrInvalidFieldLength', preventing the processing of malformed invoices.
• Payment Secret Requirement: Introduces a requirement for a 32-byte payment secret in invoices, unless blinded paths are utilized, enhancing payment security.

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[lightninglabs-deploy]

@mpins, remember to re-request review from reviewers when ready