feat(deno): Export metrics API from Deno SDK

[github-actions]

Note

The pull request "feat(deno): Export metrics API from Deno SDK" was created by @sergical but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

Summary

• Add metrics to the @sentry/core re-export block in packages/deno/src/index.ts
• The metrics namespace is already exported from @sentry/core and re-exported by @sentry/node, but was missing from the Deno SDK

Test plan

• yarn build:dev:filter @sentry/deno passes
• cd packages/deno && yarn test — all 12 tests pass
• eslint src/index.ts — no lint issues

🤖 Generated with Claude Code

[linear]

JS-1703