feat: Extend the solver

[lewisjared]

Description

Extend the solver in preparation for adding the information for the requirement for a metric.

This adds an adapter layer for determining what providers are available. Some magic might be needed there to deal with the fact that the Metric classes may not be directly available (because the ref package is installed out of process).

Still needs in follow up PRs

• Metric Run tables
• The ability to check if a metric needs to be run
• Update the metric protocol to include the concept of inputs #15
• Loading metrics from other packages

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/

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