Refactor database adapter methods

Standardized handling of database results in MySQL and Postgres adapters by using `and_then` instead of a combination of `map` and `flatten`. Shifted position of `clear` method in InMemory adapter for consistency. Also, removed unnecessary reference in Postgres adapter's delete query binding.

src/store/adapter/inmemory/inmemory.rs

@@ -41,17 +41,17 @@ impl Store for InMemoryStore {
         Ok(())
     }
 
-    async fn clear(&self) -> Result<(), StoreError> {
-        let mut db_lock = self.db.lock().await;
-        db_lock.clear();
-        Ok(())
-    }
-
     async fn remove_many(&self, keys: &[&str]) -> Result<(), StoreError> {
         let mut db_lock = self.db.lock().await;
         for key in keys {
             db_lock.remove(&key.to_string());
         }
         Ok(())
     }
+
+    async fn clear(&self) -> Result<(), StoreError> {
+        let mut db_lock = self.db.lock().await;
+        db_lock.clear();
+        Ok(())
+    }
 }

src/store/adapter/mysql/mysql.rs

@@ -91,8 +91,7 @@ impl Store for MySqlStore {
             .map_err(|_| StoreError::QueryError("Failed to fetch the value".to_string()))?;
 
         Ok(result
-            .map(|row| serde_json::from_str(row.get("value")).ok())
-            .flatten())
+            .and_then(|row| serde_json::from_str(row.get("value")).ok()))
     }
 
     async fn set(&self, key: &str, value: Value, ttl: Option<u64>) -> Result<(), StoreError> {

src/store/adapter/postgres/postgres.rs

@@ -64,8 +64,7 @@ impl Store for PostgresStore {
             .map_err(|_| StoreError::QueryError("Failed to fetch the value".to_string()))?;
 
         Ok(result
-            .map(|row| serde_json::from_str(row.get("value")).ok())
-            .flatten())
+            .and_then(|row| serde_json::from_str(row.get("value")).ok()))
     }
 
     async fn set(&self, key: &str, value: Value, ttl: Option<u64>) -> Result<(), StoreError> {
@@ -105,7 +104,7 @@ impl Store for PostgresStore {
         let query = format!("DELETE FROM {} WHERE key = ANY($1)", self.get_table_name());
 
         sqlx::query(&query)
-            .bind(&keys)
+            .bind(keys)
             .execute(&*self.pool)
             .await
             .map_err(|_| StoreError::QueryError("Failed to remove the keys".to_string()))?;