fix: exclude relative imports from tracing interception

[svelte-triage-bot]

Closes #17004.

Problem

The observability quickstart used a bare import-in-the-middle register() call. This caused relative server chunks to be wrapped, snapshotting Svelte's mutable ssr_context ESM export and crashing SSR components that call onDestroy.

Fix

• Configure synchronous import-in-the-middle registration to exclude relative imports.
• Apply the same configuration to the supported-Node branch of the fallback example.
• Document why application and framework chunks must not be intercepted.
• Add regression coverage for tracing with experimental async SSR and onDestroy.

Verification

• Focused Playwright regression: 2 passed
• pnpm -F @sveltejs/kit test:unit
• pnpm -F test-basics check
• pnpm lint
• pnpm check
• pnpm format

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from f2eeb2c:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/f2eeb2cffedaf952865b3781e86a5cda8f7d135a

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/17005

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.