Add progress tracking to tasks and turn advancement

- Extend the `Task` trait with methods for progress handling and
  completion.
- Update `DiggingTask` to store `progress` and `tick_increase`, and
  implement the new trait methods.
- Implement the new methods in the `Tasks` enum, adding a mutable
  accessor.
- Introduce `BoardState::get_active_tasks` and
  `BoardState::advance_turn` to iterate over active tasks and update
  their progress each turn.
- Un-comment the call to `board.advance_turn()` in
  `SkirmishState::tick_update`.

src/app/states/skirmish_states/tasks/digging.rs

@@ -1,15 +1,20 @@
-use std::collections::VecDeque;
-
 use crate::app::states::skirmish_states::tasks::Task;
+use std::{collections::VecDeque, ops::Add};
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct DiggingTask {
     path: VecDeque<(usize, usize)>,
+    progress: f32,
+    tick_increase: f32,
 }
 
 impl DiggingTask {
-    pub fn new(path: VecDeque<(usize, usize)>) -> Self {
-        Self { path }
+    pub fn new(path: VecDeque<(usize, usize)>, tick_increase: f32) -> Self {
+        Self {
+            path,
+            progress: 0.0,
+            tick_increase,
+        }
     }
 }
 
@@ -29,4 +34,16 @@ impl Task for DiggingTask {
     fn get_path_back_coords(&self) -> &(usize, usize) {
         self.path.back().map_or(&(0, 0), |c| c)
     }
+
+    fn get_progress(&self) -> f32 {
+        self.progress
+    }
+
+    fn progress(&mut self) {
+        let _ = self.progress.add(self.tick_increase).max(0.0).min(100.0);
+    }
+
+    fn is_finished(&self) -> bool {
+        self.progress >= 100.0
+    }
 }