Improve Value Stream Dashboard fractional precision

What does this MR do and why?

Resolves: #384350 (closed)

Increases the granularity of small metrics on the Value Stream Dashboard by revealing more fractional digits for small numbers:

1. If value is zero, show 1 digits after the decimal point.
2. If value is more than 1.0, show 1 digits after the decimal point.
3. If value is less than 1.0, show 2 digits after the decimal point.
4. If value is less than 0.1, show 3 digits after the decimal point.
5. If value is less than 0.01, show 4 digits after the decimal point.

I decided to move the unit formatter helpers out of constants and into utils. This was necessary to prevent a circular dependancy between the two files, and it feels like a more appropriate place for it to live anyways.

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Seed cycle analytics data
• Create an environment from the UI named production
• Open the rails console

  $ rails c

• Seed DORA daily metrics in the environment using the new environment

  // Within the rails console
  $ e = Environment.order(:id)[-1]
  $ 100.times { |i| Dora::DailyMetrics.create(environment_id: e.id, date: (i + 1).days.ago, deployment_frequency: rand(50), incidents_count: rand(5), lead_time_for_changes_in_seconds: rand(50000), time_to_restore_service_in_seconds: rand(100000)) }

• Enable the Exec dashboard

  Feature.enable(:group_analytics_dashboards_page)

• Visit the exec dashboard: http://gdk.test:3000/groups/${YOUR_GROUP}/-/analytics/dashboards

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.