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/infrastructure/SystemOperations/ISystemOperations.ts

@@ -19,6 +19,6 @@ export interface ICommandOps {
 
 export interface IFileSystemOps {
   setFilePermissions(filePath: string, mode: string | number): Promise<void>;
-  createDirectory(directoryPath: string, isRecursive?: boolean): Promise<string>;
+  createDirectory(directoryPath: string, isRecursive?: boolean): Promise<void>;
   writeToFile(filePath: string, data: string): Promise<void>;
 }