Refactor SQL queries into a dedicated module

- Moved SQL queries from multiple worker files into `src/worker/sql.rs` for better organization and maintainability.
- Updated references in `stockage_manager.rs`, `transport.rs`, `underground.rs`, `user_character.rs`, and `value_recalculation.rs` to use the new centralized SQL queries.
- Improved code readability by replacing `.get(0)` with `.first()` for better clarity when retrieving the first row from query results.
- Cleaned up unnecessary comments and consolidated related SQL queries.

src/worker/underground.rs

@@ -190,7 +190,7 @@ impl UndergroundWorker {
         let task_type = r.get("underground_type").cloned().unwrap_or_default();
         let params = r.get("parameters").cloned().unwrap_or_else(|| "{}".into());
 
-        Ok(Self::handle_task(pool, &task_type, performer_id, victim_id, &params)?)
+    Self::handle_task(pool, &task_type, performer_id, victim_id, &params)
     }
 
     fn handle_task(
@@ -348,7 +348,7 @@ impl UndergroundWorker {
         let rows = conn.execute("ug_select_char_user", &[&character_id])?;
 
         Ok(rows
-            .get(0)
+            .first()
             .and_then(|r| r.get("user_id"))
             .and_then(|v| v.parse::<i32>().ok())
             .unwrap_or(-1))
@@ -513,10 +513,10 @@ impl UndergroundWorker {
 
         let mut out = Vec::new();
         for r in rows {
-            if let Some(t) = r.get("stock_type_id").and_then(|v| v.parse::<i32>().ok()) {
-                if allowed.contains(&t) {
-                    out.push(r.clone());
-                }
+            if let Some(t) = r.get("stock_type_id").and_then(|v| v.parse::<i32>().ok())
+                && allowed.contains(&t)
+            {
+                out.push(r.clone());
             }
         }
         out