feat: Cookie consent exposure handling

[tyiuhc]

Summary

This update will support consent-aware firing of $impression events.

Behavior in different states:

1. GRANTED: will fire events as normal - immediately when variant actions are applied
2. REJECTED: script will not be run
3. PENDING: events will be stored in memory, and only fired when consent status is changed to GRANTED

$impression events are update to contain a timestamp to indicate when the event occurred, which will override the timestamp generated by the analytics-browser upon processing. (Relevant PR1, PR2). This is necessary for timestamp accuracy for delayed $impression firing during the PENDING state.

Checklist

• Does your PR title have the correct title format?
• Does your PR have a breaking change?: No

[promptless]

📝 Documentation updates detected!

Updated existing suggestion: Document cookie consent handling for Experiment JavaScript SDK