fix: add diagnostics + retry logic to isEnabled and getTopLevelDomain

[daniel-graham-amplitude]

Summary

• Harden the "isEnabled" function to reduce the likelihood of false negatives
  • Add 3 retries with 100 ms in between to confirm the failure isn't a "one-off"
• Add "diagnostics" to "isEnabled" and "getTopLevelDomain" so that we can monitor when either of them unexpectedly fails and can find out sooner

Checklist

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

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Note

Medium Risk
Touches cross-window postMessage handling, dynamic script loading, and cookie-detection logic; bugs here could affect instrumentation startup, diagnostics noise, or cookie persistence across many browser environments.

Overview
Introduces a new cross-window messaging layer in analytics-core (BaseWindowMessenger, getOrCreateWindowMessenger, and enableBackgroundCapture) and exports shared origin/script constants, enabling autocapture and session replay to share a singleton messenger, dedupe script loads, and avoid handler race conditions.

Hardens cookie-related behavior: CookieStorage.isEnabled() now retries and caches successful results, and both cookie enablement and getTopLevelDomain() failures can emit diagnostics events (with getTopLevelDomain() now accepting a diagnostics client). Uncaught SDK error diagnostics now track multiple loader script URLs instead of a single URL.

plugin-autocapture-browser is refactored to use the shared messenger (replacing WindowMessenger with enableVisualTagging + core singleton), adds background-capture actions, and updates text extraction to avoid cloneNode side effects; session-replay-browser enables background capture when opened via window.opener. Includes version/CDN snippet updates across packages and minor dependency lockfile bumps.

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[lewgordon-amplitude]

LGTM!