scheme: impl random + fix single schemes

src/caelestia/utils/scheme.py

@@ -1,4 +1,5 @@
 import json
+import random
 from pathlib import Path
 
 from caelestia.utils.material import get_colours_for_image
@@ -106,6 +107,13 @@ class Scheme:
                 f,
             )
 
+    def set_random(self) -> None:
+        self._name = random.choice(get_scheme_names())
+        self._flavour = random.choice(get_scheme_flavours())
+        self._mode = random.choice(get_scheme_modes())
+        self._update_colours()
+        self.save()
+
     def _check_flavour(self) -> None:
         global scheme_flavours
         scheme_flavours = None