Refactor skirmish tasks and update dependencies

- Disable automatic board.advance_turn and replace it with explicit unit
  movement handling.
- Add Tunnel structure creation during digging tasks.
- Extend DiggingTask with pop_front and current_target helpers.
- Rename task getters to get_ref_tasks and add mutable get_mut_tasks.
- Update Unit trait and Units enum to expose these new methods.
- Remove unused EMPTY_TASKS lazy static.
- Bump flake.lock revisions, hashes, and timestamps for several
  dependencies.

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

@@ -79,10 +79,14 @@ impl Unit for MinerUnit {
         self.coords
     }
 
-    fn get_tasks(&self) -> &VecDeque<Tasks> {
+    fn get_ref_tasks(&self) -> &VecDeque<Tasks> {
         &self.tasks
     }
 
+    fn get_mut_tasks(&mut self) -> &mut VecDeque<Tasks> {
+        &mut self.tasks
+    }
+
     fn get_tasks_formatted(&self) -> Vec<Line<'_>> {
         Vec::from(
             self.tasks