refactor: locally scope s3 metrics

[skl]

• Fix typo: NextScrapeGuage is now NextScrapeGauge
• Refactored package-level metrics instances into a new Metrics type, which is recreated on each test case
• Updated all test cases to include all metrics except NextScrapeGuage, now that request errors and total metric are independent.
  • N.B. results with two pages case now shows 2 requests

[Pokom]

Ah this is a nice cleanup! It's a big diff but pretty clear what's happening. I've taken a few attempts at refactoring how we emit metrics to passing in a channel and emitting new const metrics to the channel, this will make it much easier for that refactor to happen since we have tests 😄