Function metrics_middleware 

pub async fn metrics_middleware(
    __arg0: State<Arc<MetricsState>>,
    req: Request,
    next: Next,
) -> Response

Metrics middleware that records HTTP request metrics.

Records the following metrics:

• http_requests_total: Total number of HTTP requests (counter)
• http_request_duration_seconds: Request duration (gauge)
• http_errors_total: Total number of error responses (counter)