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/infrastructure/RuntimeEnvironment/RuntimeEnvironment.spec.ts

@@ -16,7 +16,7 @@ describe('RuntimeEnvironment', () => {
         const absentWindow = absentValue;
         // act
         const act = () => createEnvironment({
-          window: absentWindow,
+          window: absentWindow as never,
         });
         // assert
         expect(act).to.throw(expectedError);
@@ -123,7 +123,7 @@ describe('RuntimeEnvironment', () => {
           // arrange
           const expectedValue = undefined;
           const windowWithAbsentOs = {
-            os: absentValue,
+            os: absentValue as never,
           };
           // act
           const sut = createEnvironment({