Add Miner stats and conditional audio flag

- Extend MinerUnit with hp, digging ability, and power, and provide
  getters for these fields.
- Update the Unit trait and Units enum to expose hp, max hp,
  can_dig, and digging_power, and enhance base_text to display them.
- Remove unnecessary `Eq` derives from several structs and enums.
- Introduce a `--disable-audio` CLI flag and conditionally spawn the
  audio thread based on its value.

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

@@ -1,13 +1,21 @@
 use crate::app::states::skirmish_states::{Players, units::Unit};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub struct MinerUnit {
     owner: Players,
+    hp: u16,
+    can_dig: bool,
+    digging_power: f32,
 }
 
 impl MinerUnit {
     pub fn new(owner: Players) -> Self {
-        Self { owner }
+        Self {
+            owner,
+            hp: 100,
+            can_dig: true,
+            digging_power: 0.55,
+        }
     }
 }
 
@@ -23,4 +31,20 @@ impl Unit for MinerUnit {
     fn get_name(&self) -> &'static str {
         "Miner"
     }
+
+    fn get_hp(&self) -> u16 {
+        self.hp
+    }
+
+    fn get_max_hp(&self) -> u16 {
+        100
+    }
+
+    fn get_can_dig(&self) -> bool {
+        self.can_dig
+    }
+
+    fn get_digging_power(&self) -> f32 {
+        self.digging_power
+    }
 }