feat(unity): add telemetry to Unity SDK

[nicklasl]

Summary

• Add opt-out telemetry for Unity resolve latency and evaluation outcomes
• Upload JSON directly to the telemetry endpoint, matching confidence-sdk-js
• Bound the shared buffer at 100 traces and flush on capacity, a jittered 30-second cadence, and application lifecycle events
• Keep uploads single-flight and best-effort, with bounded exponential retry
• Use canonical telemetry enum values and structured evaluation results

Test plan

• Build with warnings as errors
• Focused Unity telemetry and endpoint tests (17 passed)
• Unity Editor build (Unity is unavailable locally)