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/application/Parser/Script/Validation/CodeValidator.ts

@@ -9,7 +9,7 @@ export class CodeValidator implements ICodeValidator {
     code: string,
     rules: readonly ICodeValidationRule[],
   ): void {
-    if (!rules || rules.length === 0) { throw new Error('missing rules'); }
+    if (rules.length === 0) { throw new Error('missing rules'); }
     if (!code) {
       return;
     }

src/application/Parser/Script/Validation/Rules/NoDuplicatedLines.ts

@@ -3,9 +3,7 @@ import { ICodeLine } from '../ICodeLine';
 import { ICodeValidationRule, IInvalidCodeLine } from '../ICodeValidationRule';
 
 export class NoDuplicatedLines implements ICodeValidationRule {
-  constructor(private readonly syntax: ILanguageSyntax) {
-    if (!syntax) { throw new Error('missing syntax'); }
-  }
+  constructor(private readonly syntax: ILanguageSyntax) { }
 
   public analyze(lines: readonly ICodeLine[]): IInvalidCodeLine[] {
     return lines