refactor(sql): do not expose rusqlite Error type in query_map methods

We use query_and_then() instead of query_map() function now.
The difference is that row processing function
returns anyhow::Result, so simple fallible processing
like JSON parsing can be done inside of it
when calling query_map_vec() and query_map_collect()
without having to resort to query_map()
and iterating over all rows again afterwards.

src/mimeparser.rs

@@ -357,7 +357,10 @@ impl MimeMessage {
         let decrypted_msg; // Decrypted signed OpenPGP message.
         let secrets: Vec<String> = context
             .sql
-            .query_map_vec("SELECT secret FROM broadcast_secrets", (), |row| row.get(0))
+            .query_map_vec("SELECT secret FROM broadcast_secrets", (), |row| {
+                let secret: String = row.get(0)?;
+                Ok(secret)
+            })
             .await?;
 
         let (mail, is_encrypted) =