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.

tests/unit/shared/Stubs/CategoryDataStub.ts

@@ -1,8 +1,8 @@
 import type { CategoryData, CategoryOrScriptData, DocumentationData } from '@/application/collections/';
-import { ScriptDataStub } from './ScriptDataStub';
+import { createScriptDataWithCode } from '@tests/unit/shared/Stubs/ScriptDataStub';
 
 export class CategoryDataStub implements CategoryData {
-  public children: readonly CategoryOrScriptData[] = [ScriptDataStub.createWithCode()];
+  public children: readonly CategoryOrScriptData[] = [createScriptDataWithCode()];
 
   public category = 'category name';