I updated the Rollout interface to allow optional traits property, and updated resolveState to handle traits.
Quick notes on traits:
session traits are array of strings, each string is considered one trait (similar to the tag concept)
a Rollout variant will only match if all the Rollout.traits are found in the session traits (so Rollout.traits ["a","b"] matches session traits ["a","b","c"], but not session traits ["a"]
If multiple Rollout variants match, most matching traits take precedence;
If still multiple Rollout variants tied, the "value":false once take precedence (allow developers to explicitly ensure certain features are turned off even if other matches would have allow it on)
If still multiple Rollout variants tied, the higher value of the percentage will take precedence