A/B testing framework

[ibrahimcesar]

Description

Add A/B testing capabilities to telemetry-kit for feature experimentation.

Features

• Experiment definition API
• Variant assignment (consistent per user)
• Exposure tracking
• Conversion tracking
• Statistical significance calculation

Example Usage

```rust
let variant = telemetry.get_variant("checkout-redesign")?;

match variant.as_str() {
"control" => show_old_checkout(),
"treatment" => show_new_checkout(),
_ => show_old_checkout(),
}

// Track conversion
telemetry.track_conversion("checkout-redesign", variant)?;
```

Privacy Considerations

• Variants assigned using anonymous user ID
• No PII required for experimentation
• Compliant with DO_NOT_TRACK

Acceptance Criteria

• Simple API for experiments
• Dashboard for experiment analysis
• Privacy-preserving implementation