Initial implementation of BOLT 12 payer proof test vector CLI

Add a Rust CLI tool that generates and verifies test vectors for BOLT 12
payer proofs as specified in lightning/bolts#1295. The tool uses the
rust-lightning implementation from lightningdevkit/rust-lightning#4297.

Features:
- Generate deterministic test vectors with configurable seed
- Verify test vectors from JSON files
- Support for basic proofs, proofs with notes, and invalid test cases
- Uses refund flow for explicit payer key control

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: vincenzopalazzo

.gitignore

@@ -0,0 +1,5 @@
+/target
+
+# Generated test vector files
+test_vectors.json
+test_output.json