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/shared/Stubs/SharedFunctionCollectionStub.ts

@@ -1,6 +1,6 @@
-import { ISharedFunction, FunctionBodyType } from '@/application/Parser/Script/Compiler/Function/ISharedFunction';
+import { ISharedFunction } from '@/application/Parser/Script/Compiler/Function/ISharedFunction';
 import { ISharedFunctionCollection } from '@/application/Parser/Script/Compiler/Function/ISharedFunctionCollection';
-import { SharedFunctionStub } from './SharedFunctionStub';
+import { createSharedFunctionStubWithCode } from './SharedFunctionStub';
 
 export class SharedFunctionCollectionStub implements ISharedFunctionCollection {
   private readonly functions = new Map<string, ISharedFunction>();
@@ -13,10 +13,11 @@ export class SharedFunctionCollectionStub implements ISharedFunctionCollection {
   }
 
   public getFunctionByName(name: string): ISharedFunction {
-    if (this.functions.has(name)) {
-      return this.functions.get(name);
+    const foundFunction = this.functions.get(name);
+    if (foundFunction) {
+      return foundFunction;
     }
-    return new SharedFunctionStub(FunctionBodyType.Code)
+    return createSharedFunctionStubWithCode()
       .withName(name)
       .withCode('code by SharedFunctionCollectionStub')
       .withRevertCode('revert-code by SharedFunctionCollectionStub');