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/application/Parser/Script/Validation/Rules/NoEmptyLines.spec.ts

@@ -23,12 +23,6 @@ describe('NoEmptyLines', () => {
         expected: [2, 4].map((index) => ({ index, error: 'Empty line' })),
         sut: new NoEmptyLines(),
       },
-      {
-        testName: 'shows error for undefined and null lines',
-        codeLines: ['first line', undefined, 'third line', null],
-        expected: [2, 4].map((index) => ({ index, error: 'Empty line' })),
-        sut: new NoEmptyLines(),
-      },
       {
         testName: 'shows error for whitespace-only lines',
         codeLines: ['first line', '  ', 'third line'],