📚 Add state management and testing guidelines documentation

Introduced new documentation files for state management and testing guidelines to enhance developer understanding and best practices.

- 📚 **Docs**: Added state management guidelines with local and global state recommendations
- 📚 **Docs**: Created testing guidelines including unit testing requirements and best practices
- 📚 **Docs**: Updated project structure documentation for clarity

docs/guidelines/testing.md

@@ -0,0 +1,35 @@
+# Testing Guidelines
+
+## Unit Testing Requirements
+
+- Test files should end with `.spec.ts`.
+- Use Spectator for Component, Directive and Service tests.
+- Use Jest as the test runner.
+- Follow the Arrange-Act-Assert (AAA) pattern in tests.
+- Mock external dependencies to isolate the unit under test.
+
+## Example Test Structure
+
+```typescript
+import { createComponentFactory, Spectator } from '@ngneat/spectator/jest';
+import { MyComponent } from './my-component.component';
+
+describe('MyComponent', () => {
+  let spectator: Spectator<MyComponent>;
+  const createComponent = createComponentFactory(MyComponent);
+
+  beforeEach(() => {
+    spectator = createComponent();
+  });
+
+  it('should create', () => {
+    expect(spectator.component).toBeTruthy();
+  });
+
+  it('should handle action correctly', () => {
+    spectator.setInput('inputProp', 'testValue');
+    spectator.click('button');
+    expect(spectator.component.outputProp).toBe('expectedValue');
+  });
+});
+```