dynamic traits are not supported yet

## Middleware is an interface for processing HTTP requests.
## Each middleware in the chain can modify the request and response.
trait Middleware:
    fn set_next(self, next: Middleware):
        ...
    fn call(self, context: Context) -> HTTPResponse:
        ...

## MiddlewareChain is a chain of middleware that processes the request.
## The chain is a linked list of middleware objects.
struct MiddlewareChain(HTTPService):
    var root: Middleware

    fn add(self, middleware: Middleware):
        if self.root == nil:
            self.root = middleware
        else:
            var current = self.root
            while current.next != nil:
                current = current.next
            current.set_next(middleware)

    fn call(self, request: HTTPRequest) raises -> HTTPResponse:
        var context = Context(request)
        return self.root.call(context)

  var middleware = MiddlewareChain()
  middleware.add(CompressionMiddleware())
  middleware.add(ErrorMiddleware())
  middleware.add(LoggerMiddleware())
  middleware.add(CorsMiddleware(allows_origin = "*"))
  middleware.add(BasicAuthMiddleware("admin", "password"))
  middleware.add(StaticMiddleware("static"))
  middleware.add(router)
  middleware.add(NotFoundMiddleware())