Instrument web checkout failures

[tiagocandido]

Summary

• Record Web checkout errors, protocol decoding failures, and navigation duration (Web has no navigation retry path)
• Add a default-on telemetry setting with immediate runtime opt-out that discards buffered and active work
• Scope the telemetry client to each connected element, shut it down on disconnect, and flush with keepalive on pagehide
• Measure navigation from window.open, record only genuine success or terminal failure, and exclude dismissal/unmount paths
• Treat every ec.error as terminal for the embedded session, matching the native SDKs: the checkout window now closes on any ec.error, not only unrecoverable severities
• Keep unit tests on a stubbed telemetry transport so test runs can never post metrics
• Document the bounded diagnostic data and explicit opt-out

Validation

• Formatting, lint, and TypeScript checks
• Web unit tests
• Production package and declaration build