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/cli.rs

@@ -150,6 +150,14 @@ pub struct Cli {
         )]
     pub soundtrack: Soundtrack,
 
+    /// Disable soundtrack (default: disabled).
+    #[arg(
+        long,
+        help = "Disable soundtrack (default: disable)",
+        default_value_t = false
+    )]
+    pub disable_audio: bool,
+
     /// Mute soundtrack (default: disabled).
     #[arg(
         long,