Add rln-cli command-line interface and Makefile support

- Introduced `rln-cli` as a new binary for interacting with the RGB Lightning Node.
- Added a Makefile for building, testing, and running the CLI and node.
- Updated `Cargo.toml` to include `rln-cli` and new dependencies.
- Enhanced `README.md` with CLI usage instructions and examples.
- Created a demo script for showcasing common CLI operations.
- Added integration tests for CLI commands to ensure functionality.

fix linting

Author: bitwalt

src/test/cli_integration.rs

@@ -611,7 +611,7 @@ async fn cli_onchain_list_transactions() {
 
     let json = result.unwrap();
     let transactions = json["transactions"].as_array().unwrap();
-    assert!(transactions.len() > 0);
+    assert!(!transactions.is_empty());
 }
 
 #[serial_test::serial]
@@ -634,7 +634,7 @@ async fn cli_onchain_list_unspents() {
 
     let json = result.unwrap();
     let unspents = json["unspents"].as_array().unwrap();
-    assert!(unspents.len() > 0);
+    assert!(!unspents.is_empty());
 }
 
 #[serial_test::serial]