FFM-11211 Metrics enhancements

[erdirowlands]

What

• Splits evaluation and target metrics into their own caches:

  • So that evaluations can be keyed on flag + variation and that we can track target metrics separately because we use the global target for evaluations

• Implement seen targets - this was previously implemented but not working:

  • ensures that the metrics service only gets sent target metrics for a target once, for the lifetime of the SDK instance
  • ensures that the SDK processes truly unique targets fairly, and that old targets don't occupy the 100K limit set per

• No longer flushes metrics if map is full, but instead logs a warning and returns.

Testing

• Metrics accuracy:
  • TestGrid metrics tests
  • Manual sample app
  • Non-anonymous targets appear in UI
  • Anonymous targets don't appear in UI
• SeenTargets:
  • Manual testing
• Evaluation limits
  • Manual