process_cpu_seconds_total is incorrectly registered as an IntCounter

[odevices]

https://github.com/tikv/rust-prometheus/blob/81514180fc47ed387d20140119b97c33495f85fe/src/process_collector.rs#L43C1-L53C1

        let cpu_total = IntCounter::with_opts(
            Opts::new(
                "process_cpu_seconds_total",
                "Total user and system CPU time spent in \
                 seconds.",
            )
            .namespace(namespace.clone()),
        )
        .unwrap();
        descs.extend(cpu_total.desc().into_iter().cloned());

This needs to be reported as a float, otherwise the rate queries are broken. Consider that the promotheus server self-reports this metric in floats.

[ti-chi-bot]

Welcome @odevices! It looks like this is your first issue to tikv/rust-prometheus 🎉

[odevices]

Here is what I mean.
prometheus - self-reported metrics
bbsrv - a rust rest api server using the prometheus crate to report process metrics