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/NodeValidation/NodeValidator.spec.ts

@@ -1,7 +1,7 @@
 import { describe, it, expect } from 'vitest';
 import { NodeDataError } from '@/application/Parser/NodeValidation/NodeDataError';
 import { NodeValidator } from '@/application/Parser/NodeValidation/NodeValidator';
-import { expectDeepThrowsError } from '@tests/unit/shared/Assertions/ExpectDeepThrowsError';
+import { expectDeepThrowsError } from '@tests/shared/Assertions/ExpectDeepThrowsError';
 import { CategoryDataStub } from '@tests/unit/shared/Stubs/CategoryDataStub';
 import { NodeDataErrorContextStub } from '@tests/unit/shared/Stubs/NodeDataErrorContextStub';
 import { NodeData } from '@/application/Parser/NodeValidation/NodeData';

tests/unit/application/Parser/NodeValidation/NodeValidatorTestRunner.ts

@@ -2,7 +2,7 @@ import { describe, it } from 'vitest';
 import { NodeDataError, INodeDataErrorContext } from '@/application/Parser/NodeValidation/NodeDataError';
 import { NodeData } from '@/application/Parser/NodeValidation/NodeData';
 import { getAbsentObjectTestCases, getAbsentStringTestCases, itEachAbsentTestCase } from '@tests/unit/shared/TestCases/AbsentTests';
-import { expectDeepThrowsError } from '@tests/unit/shared/Assertions/ExpectDeepThrowsError';
+import { expectDeepThrowsError } from '@tests/shared/Assertions/ExpectDeepThrowsError';
 
 export interface ITestScenario {
   readonly act: () => void;