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/FileSystemOpsStub.ts

@@ -12,12 +12,12 @@ export class FileSystemOpsStub
     return Promise.resolve();
   }
 
-  public createDirectory(directoryPath: string, isRecursive?: boolean): Promise<string> {
+  public createDirectory(directoryPath: string, isRecursive?: boolean): Promise<void> {
     this.registerMethodCall({
       methodName: 'createDirectory',
       args: [directoryPath, isRecursive],
     });
-    return Promise.resolve(directoryPath);
+    return Promise.resolve();
   }
 
   public writeToFile(filePath: string, data: string): Promise<void> {