Disable prom metrics in `parser` package

[aberry-21]

I'm not using seq-db fully - only the parser. I don't need the metrics, I'd like to disable them, but there's no such option. Is it possible to add this feature?

[dkharms]

Hey!

First, I've updated the title and description of the issue, since we communicate in English here.

Second, this isn't a use case we have or plan to support -- the parser is part of our internal implementation and may (and will) change in backwards-incompatible ways.

That said, I see two options:

• You can submit a pull request if you'd like to (though the caveat above still applies).
• You can copy the parser implementation into your own project -- seq-db's license permits this.

If you do go with a pull request, please follow our current convention for metrics: we place all metrics in a separate metrics.go file within the package they belong to.