feat: Refactor example page and showcase components

- Updated ExamplePage to use a single Showcase component instead of separate InputShowCase and FormShowcase components.
- Added CheckboxShowcase, FormShowcase, and InputShowCase components to the showcase directory.
- Implemented Checkbox component with various states and styles.
- Enhanced InputShowCase to demonstrate different input types and states.
- Integrated new styles for checkbox variants and states.
- Updated package dependencies to include @rc-component/checkbox.

packages/ui/package.json

@@ -12,6 +12,7 @@
     "test:watch": "vitest --watch"
   },
   "dependencies": {
+    "@rc-component/checkbox": "^1.0.1",
     "@rc-component/form": "^1.6.2",
     "@rc-component/input": "^1.1.2",
     "@rc-component/input-number": "^1.6.2",