feat: Updates to Provider module in preparation for InMemoryProvider

[maxveldink]

This PR

• Fixes two bugs I encountered during local development (bin/console not loading and a memorization issue with Configuration
• Adds constants for Reason and ErrorCode enumerations
• Refactored ResolutionDetails up a module layer, and updated the client to return an EvaluationDetails struct, matching a callout from a spec:

The resolution details structure is not exposed to the Application Author. It defines the data which Provider Authors must return when resolving the value of flags.

(Note at the bottom of this section)

Follow-up Tasks

• Following this PR, I will PR the InMemoryProvider that I've been working on to satisfy a utility in Appendix A.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8bfe176) 98.90% compared to head (960d486) 99.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
+ Coverage   98.90%   99.22%   +0.32%     
==========================================
  Files           6       11       +5     
  Lines          91      129      +38     
==========================================
+ Hits           90      128      +38     
  Misses          1        1              

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[maxveldink]

@beeme1mr @toddbaert Before I merge in some of these PRs, I want to double-check if I need a maintainer review first or if, at the approver level, I can also merge in PRs.

[beeme1mr]

You should be able to merge whenever you're ready. Let me know if you're unable to and we'll update your permissions.