fix(kitojs): middleware propagation and mounting with router

[skick1234]

Issue

Follow router.use() docs:

  /**
   * Registers a global middleware that runs for all routes in this router.
   *
   * @param middleware - Middleware function or definition
   * @returns The router instance for chaining
   *
   * @example
   * ```typescript
   * router.use((ctx, next) => {
   *   console.log(`${ctx.req.method} ${ctx.req.url}`);
   *   next();
   * });
   * ```
   */

When using router.mount(path, subRouter), any middleware defined on the subRouter via .use() was silently ignored. Only the middleware defined directly on the routes themselves (e.g., in .get('/path', [mw], handler)) were preserved.

Key changes

• Modified mount() to retrieve the sub-router's middleware stack
• Improved path normalization to handle the root / prefix correctly
• Prepended these middlewares to every imported route, ensuring proper inheritance
• Simplified the mount override to rely on super.mount() for path prefixing and middleware merging
• Create test cases for router

[nehu3n]

Thank you so much!