feat(deno): Export metrics API from Deno SDK

The metrics namespace is already exported from @sentry/core and re-exported
by @sentry/node, but was missing from the Deno SDK.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sergical

packages/deno/src/index.ts

@@ -89,6 +89,7 @@ export {
   updateSpanName,
   wrapMcpServerWithSentry,
   featureFlagsIntegration,
+  metrics,
 } from '@sentry/core';
 
 export { DenoClient } from './client';