Refactor task handling to use VecDeque references

- Change `get_tasks` to return `&VecDeque<Tasks>` instead of a formatted
  `String`.
- Introduce `get_tasks_formatted` for display purposes.
- Update `MinerUnit`, `Unit` trait, `Units` enum, and its `Option`
  implementation accordingly.
- Add `EMPTY_TASKS` lazy static for handling empty task lists.
- Adjust `BoardState` to use the new task API (commented out
  conditional).

src/app/states/skirmish_states/units/miner.rs

@@ -57,7 +57,11 @@ impl Unit for MinerUnit {
         self.coords
     }
 
-    fn get_tasks(&self) -> String {
+    fn get_tasks(&self) -> &VecDeque<Tasks> {
+        &self.tasks
+    }
+
+    fn get_tasks_formatted(&self) -> String {
         format!("{:?}", self.tasks)
     }