Use VecDeque for tasks and marked cells

Replace `Vec` with `VecDeque` in `BoardState` marked cells,
`DiggingTask` path,
and `MinerUnit` tasks to enable efficient push/pop operations. Remove
the
`Copy` trait from several structs and enums, adjust derives accordingly,
and
use `as_ref` in `Option<Units>` implementations to avoid consuming the
option.
Update cell rendering to clone widgets and adjust
`CellWidget::get_option_unit`
to return a cloned `Option<Units>`. Add necessary `VecDeque` imports.

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

@@ -1,14 +1,12 @@
-use crate::app::widgets::CellWidget;
+use std::collections::VecDeque;
 
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct DiggingTask {
-    // path: Vec<(usize, usize)>,
+    path: VecDeque<(usize, usize)>,
 }
 
 impl DiggingTask {
-    pub fn new(path: Vec<(u16, u16)>) -> Self {
-        Self {
-            // path
-        }
+    pub fn new(path: VecDeque<(usize, usize)>) -> Self {
+        Self { path }
     }
 }

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

@@ -1,6 +1,6 @@
 use crate::app::states::skirmish_states::tasks::DiggingTask;
 
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Tasks {
     Digging(DiggingTask),
 }