fix(clippy): allow unused_async on the synchronous engine impls

src/engine/duckdb/mod.rs

@@ -39,6 +39,12 @@ pub struct DuckDbEngine;
 /// Default schema used when no `--schema` is provided.
 const DEFAULT_SCHEMA: &str = "main";
 
+// `DatabaseEngine` declares these methods as returning futures, so each impl must be
+// `async` whether or not its body awaits. The DuckDB driver is synchronous, so all three
+// methods here have no `.await` and trip `clippy::unused_async` -- a lint that cannot be
+// satisfied without hand-rolling `impl Future` bodies purely to appease it. The
+// `postgres` and `mysql` impls are unaffected because their drivers genuinely await.
+#[allow(clippy::unused_async)]
 impl DatabaseEngine for DuckDbEngine {
     async fn validate_connection(config: &ConnectionConfig) -> Result<ConnectionInfo> {
         let file_path = extract_file_path(config)?;

src/engine/sqlite/mod.rs

@@ -31,6 +31,12 @@ use crate::error::{PlenumError, Result};
 /// `SQLite` database engine implementation
 pub struct SqliteEngine;
 
+// `DatabaseEngine` declares these methods as returning futures, so each impl must be
+// `async` whether or not its body awaits. The SQLite driver is synchronous, so all three
+// methods here have no `.await` and trip `clippy::unused_async` -- a lint that cannot be
+// satisfied without hand-rolling `impl Future` bodies purely to appease it. The
+// `postgres` and `mysql` impls are unaffected because their drivers genuinely await.
+#[allow(clippy::unused_async)]
 impl DatabaseEngine for SqliteEngine {
     async fn validate_connection(config: &ConnectionConfig) -> Result<ConnectionInfo> {
         // Validate config is for SQLite