Collect metrics on scrape instead of timer

The prometheus docs on exporters say:

Metrics should only be pulled from the application when Prometheus scrapes them, exporters should not perform scrapes based on their own timers. That is, all scrapes should be synchronous.

The very first example provided by this repository goes against those docs by just spamming the same function on a timer.

Can anyone provide a basic example that shows how to start a metrics collection only when prometheus connects to the exporter, as it's actually supposed to be done? Because christ, it's faster to just set up a flask server with a custom /metrics endpoint than actually figure out how to do so using this framework.

Comienza con la documentación sobre la programación de Prometheus exporter y el primer ejemplo del repositorio, que el issue identifica como basado en un temporizador. Añade un ejemplo básico que muestre que la recopilación comienza de forma síncrona cuando Prometheus hace scrape del exporter; se considera terminado cuando el ejemplo ya no realiza la recopilación con su propio temporizador.