refactor(report): replaces metrics formatting code with Intl API calls

[sverweij]

Description

• replaces the instability metrics formatting code with an Intl function call

Motivation and Context

• reduces maintenance
• output is localized, so at least in theory easier to grasp for the reader

How Has This Been Tested?

• green ci
• adapted unit tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Documentation only change
• Refactor (non-breaking change which fixes an issue without changing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• 📖

  • My change doesn't require a documentation update, or ...
  • it does and I have updated it

• ⚖️

  • The contribution will be subject to The MIT license, and I'm OK with that.
  • The contribution is my own original work.
  • I am ok with the stuff in CONTRIBUTING.md.