[CV2ResultsViewer] Add callback support

src/polystar/view/cv2_results_viewer.py

+from contextlib import suppress
+from typing import Any, Callable, Dict
+
 import cv2
 import numpy as np
 
@@ -23,10 +26,12 @@ COLORS = [
     (23, 190, 207),
 ]  # seaborn.color_palette() * 255
 
+Callback = Callable[[], Any]
+
 
 class CV2ResultViewer(ResultViewerABC):
-    def __init__(self, name: str, delay: int = 1, end_keys: str = "q"):
-        self.end_keys = [ord(c) for c in end_keys]
+    def __init__(self, name: str, delay: int = 1, end_key: str = "q", key_callbacks: Dict[str, Callback] = None):
+        self.keycode_callbacks = self._make_keycode_callbacks(end_key, key_callbacks or {})
         self.delay = delay
         self.name = name
         self._current_image: Image = None
@@ -70,4 +75,13 @@ class CV2ResultViewer(ResultViewerABC):
 
     def display(self):
         cv2.imshow(self.name, self._current_image)
-        self.finished = cv2.waitKey(self.delay) & 0xFF in self.end_keys
+        keycode = cv2.waitKey(self.delay) & 0xFF
+        with suppress(KeyError):
+            self.keycode_callbacks[keycode]()
+
+    def stop(self):
+        self.finished = True
+
+    def _make_keycode_callbacks(self, end_key: str, key_callbacks: Dict[str, Callback]) -> Dict[int, Callback]:
+        key_callbacks[end_key] = self.stop
+        return {ord(k): f for k, f in key_callbacks.items()}