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/shared/Assertions/ExpectThrowsAsync.ts

@@ -1,4 +1,5 @@
 import { expect } from 'vitest';
+import { expectExists } from '@tests/shared/Assertions/ExpectExists';
 
 export async function expectThrowsAsync(
   method: () => Promise<unknown>,
@@ -10,11 +11,9 @@ export async function expectThrowsAsync(
   } catch (err) {
     error = err;
   }
-  expect(error).toBeDefined();
+  expectExists(error);
   expect(error).to.be.an(Error.name);
-  if (errorMessage) {
-    expect(error.message).to.equal(errorMessage);
-  }
+  expect(error.message).to.equal(errorMessage);
 }
 
 export async function expectDoesNotThrowAsync(