Support @koa/router@14 and @koa/router@15

**Is your feature request related to a problem? Please describe.**

@koa/router [v14.0.0](https://github.com/koajs/router/releases/tag/v14.0.0) was released in Aug 2025, [v15.0.0](https://github.com/koajs/router/releases/tag/v15.0.0) in Dec 2025. The Elastic Node.js APM agent currently still requires <14.

While we do get the majority of instrumentation with v14 or v15, it currently does not automatically assign paths as transaction names as it does in v13

**Describe the solution you'd like**
Full support for v14 and v15 of @koa/router. (Potentially also under the old name koa-router for v14)

**Describe alternatives you've considered**
Currently have to downgrade @koa/router to v13.X or add additional custom code to add transaction names.

**Additional context**

v15.0.0 drops support for node.js 18.