[BUG] `salt_version` is numeric, breaks with `3006.10`

[lkubb]

Description
The tests for #37 are failing because the value for salt_version is interpreted as a floating number, turning 3006.10 into 3006.1:

  - salt_version 3006.10
  ?                    -
  + salt_version 3006.1

I think this is caused by using a Gauge to represent this data, which is a numeric type.

I'm not a Prometheus user, hence not sure what the best course of action is here. PRs welcome. I think this extension was created by @nicholasmhughes - maybe you can find the time to chime in.

Setup
irrelevant

Steps to Reproduce the behavior
Install 3006.10. See: https://github.com/salt-extensions/saltext-prometheus/actions/runs/14120480180/job/39766356587