Refactor to enforce strictNullChecks

This commit applies `strictNullChecks` to the entire codebase to improve
maintainability and type safety. Key changes include:

- Remove some explicit null-checks where unnecessary.
- Add necessary null-checks.
- Refactor static factory functions for a more functional approach.
- Improve some test names and contexts for better debugging.
- Add unit tests for any additional logic introduced.
- Refactor `createPositionFromRegexFullMatch` to its own function as the
  logic is reused.
- Prefer `find` prefix on functions that may return `undefined` and
  `get` prefix for those that always return a value.

src/presentation/components/Scripts/Slider/SliderHandle.vue

@@ -29,7 +29,10 @@ export default defineComponent({
     const cursorCssValue = 'ew-resize';
     let initialX: number | undefined;
 
-    const resize = (event) => {
+    const resize = (event: MouseEvent) => {
+      if (initialX === undefined) {
+        throw new Error('Resize action started without an initial X coordinate.');
+      }
       const displacementX = event.clientX - initialX;
       emit('resized', displacementX);
       initialX = event.clientX;