feat: trickle events channel reader for runtime telemetry

[seanhanca]

Summary

Subscribe to the trickle events channel to capture runtime telemetry from Scope orchestrators that have PR daydreamlive/scope#1040 deployed.

Changes

• trickle_reader.py: Background async reader for the trickle events channel. Reads sequential segments, parses JSON events, collects telemetry events (PR 1040), MediaPublishStats from log lines, and lifecycle events (runner_ready, stream_started, pipeline_loaded).
• sdk_executor.py: Automatically starts the trickle reader when events_url is present in the stream start response. Attaches collected metrics to the RunResult.
• metrics_reporter.py: Includes trickle channel data (event counts, media stats, runtime telemetry) in loadtest_run_completed events sent to /v1/metrics.

How it works

Scope Runner (PR 1040) → publish_event("stream_heartbeat") → TrickleEventsSink
  → trickle events channel: {"type": "telemetry", "event": {...}}
    → TrickleEventsReader (this PR) reads segments via HTTP GET
      → TrickleMetrics collected → attached to RunResult → reported to /v1/metrics

Requires

• Orchestrators with scope#1040 deployed (orch-prod-scope-1, orch-prod-scope-vast-1)
• Network connectivity from the load test VM to those orchestrators on port 8935
• Pulumi manages the networking configuration

Tests

• 135 unit tests passing
• E2e verification pending orchestrator connectivity