style: apply rustfmt, fix clippy warnings, and minor code cleanup

Reformat Rust code with rustfmt, suppress clippy::too_many_arguments
for Tauri IPC commands, derive Default for AppSettings, fix unused
variable pattern in TableDataView, and add unit tests for utils.

src-tauri/src/commands/management.rs

@@ -336,10 +336,7 @@ pub async fn alter_role(
         options.push(format!("CONNECTION LIMIT {}", limit));
     }
     if let Some(ref valid_until) = params.valid_until {
-        options.push(format!(
-            "VALID UNTIL '{}'",
-            valid_until.replace('\'', "''")
-        ));
+        options.push(format!("VALID UNTIL '{}'", valid_until.replace('\'', "''")));
     }
 
     if !options.is_empty() {