yoda: warning cleanup sweep (dead code + clippy --fix) (squashed)

Squash of 4 yoda commits:
- 84437e21 yoda: libcosmic-yoda dead-code purge (14->0 warnings)
- 999db0a4 yoda: cosmic-theme cleanup (4->0 warnings) — workspace at 0 warnings total
- 4743bb8e yoda: cargo clippy --fix on libcosmic-yoda (115->33 warnings)
- 675f3b59 chore: reduce local stack warnings

cosmic-theme/src/output/vs_code.rs

@@ -266,6 +266,14 @@ impl From<Theme> for VsTheme {
 }
 
 impl Theme {
+    /// Write this theme to VS Code's `settings.json` as a
+    /// `workbench.colorCustomizations` entry, and enable
+    /// `window.autoDetectColorScheme` so VS Code follows the system theme.
+    ///
+    /// # Errors
+    ///
+    /// Returns an `OutputError` if the user config dir is missing, the
+    /// settings file cannot be read/written, or its JSON is invalid.
     #[cold]
     pub fn apply_vs_code(self) -> Result<(), OutputError> {
         let vs_theme = VsTheme::from(self);
@@ -291,6 +299,13 @@ impl Theme {
         Ok(())
     }
 
+    /// Remove the `workbench.colorCustomizations` entry previously written
+    /// by [`Theme::apply_vs_code`] from VS Code's `settings.json`.
+    ///
+    /// # Errors
+    ///
+    /// Returns an `OutputError` if the user config dir is missing, the
+    /// settings file cannot be read/written, or its JSON is invalid.
     #[cold]
     pub fn reset_vs_code() -> Result<(), OutputError> {
         let mut config_dir = dirs::config_dir().ok_or(OutputError::MissingConfigDir)?;