Fix: Ensure compatibility with Express 4.x and 5.x in ExpressPlugin

[thiagomatar]

We are evaluating the use of SkyWalking in our company, and I have started some proof-of-concept tests to evaluate the agents.
I created a new project using Node.js/NestJS and the SkyWalking Node.js agent, following the instructions provided on the NodeJS Agent page to install it in the project.

Versions used:

• Node.js: 22.14.0
• NestJS: 11.0.1
• Express: 5.0.1

Upon initializing the project, I encountered the following error message:

{
  message: 'Error installing plugin express *',
  level: 'error',
  file: '...node_modules/skywalking-backend-js/lib/core/PluginInstaller.js'
}

After investigating the code, I identified the root cause.
In the ExpressPlugin.js file, line 39:

var router = (_b = (_a = installer.require) === null || _a === void 0 ? void 0 : _a.call(installer, 'express/lib/router')) !== null && _b !== void 0 ? _b : require('express/lib/router');

The error Cannot find module 'express/lib/router' occurs because the installed version of Express no longer has this folder structure (express/lib/router). This is due to recent versions of Express reorganizing their modules differently.

To address this issue, I am adding compatibility for both older and newer versions of Express:

1. First, attempt to load express.Router() (used in Express 5+).
2. If that fails, attempt to load express/lib/router (used in Express 4.x).

[thiagomatar]

simplifying the solution

[thiagomatar]

sorry guys I did a mistake and I will open other PR