[refactor] clean up string formatting, improve control flow, and enhance readability in core modules and tests

tests/integration_cli.rs

@@ -340,9 +340,16 @@ fn verbosity_quiet_suppresses_logs_but_keeps_stdout() {
 
     assert!(output.status.success());
     let stdout = String::from_utf8(output.stdout).unwrap();
-    assert!(stdout.contains("\"items\""), "stdout JSON should be present in quiet mode");
+    assert!(
+        stdout.contains("\"items\""),
+        "stdout JSON should be present in quiet mode"
+    );
     let stderr = String::from_utf8(output.stderr).unwrap();
-    assert!(stderr.trim().is_empty(), "stderr should be empty in quiet mode, got: {}", stderr);
+    assert!(
+        stderr.trim().is_empty(),
+        "stderr should be empty in quiet mode, got: {}",
+        stderr
+    );
 }
 
 #[test]
@@ -363,7 +370,10 @@ fn verbosity_verbose_emits_debug_logs_on_stderr() {
     let stdout = String::from_utf8(output.stdout).unwrap();
     assert!(stdout.contains("\"items\""));
     let stderr = String::from_utf8(output.stderr).unwrap();
-    assert!(stderr.contains("Mode: merge"), "stderr should contain debug log with -v");
+    assert!(
+        stderr.contains("Mode: merge"),
+        "stderr should contain debug log with -v"
+    );
 }
 
 #[test]