`#[metrics]` Debug implementation

[mempirate]

Description

It would be nice to be able to print metrics and their values to stdout using a Debug implementation that's automatically created on macro expansion. Have to first check whether it's even possible to get the labels and raw atomic values from the prometheus metric types (Counter, Histogram etc)

[Karrq]

Could you elaborate a bit more what you'd like to see here?
For example, whenever a metric is accessed have it printed out as a tracing event?
In case of something like a histogram, what values would you like to see? Sample count per bucket? All values in buckets?

[mempirate]

For example, whenever a metric is accessed have it printed out as a tracing event?

Not sure what you mean by this. My idea is just to have the Debug impl print out the actual metric values. So if we do println!("{app_metrics:?}"), you'd see a representation of the values on stdout.

For a histogram, probably count, sum, min, max, mean, p50?

Also, since this may add some extra processing to Debug prints, this should be feature-gated.