fix(kit): ensure instrumentation file is posixified on Windows

[BastiDood]

This PR fixes a bug on Windows where SvelteKit incorrectly generates the wrong import path for the instrumentation.server.ts file. This practically broke the OpenTelemetry integration on Windows because the instrumentation.server.ts never gets called in both dev and preview.

// Expected
import './server/instrumentation.server.js';

// Actual
import './server/instrumentation\server.js';

The fix was pretty simple: posixify the relative_instrumentation path. I was unsure whether to use node:path/posix or the existing posixify utility, so I chose the latter to err on the side of existing conventions. Let me know if the former is preferred.

---

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

Edits

• Please ensure that 'Allow edits from maintainers' is checked. PRs without this option may be closed.

[changeset-bot]

🦋 Changeset detected

Latest commit: d40f12f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[BastiDood]

Not sure why only one of the CI runs timed out, but I think it's safe to retry?

[teemingc]

Thanks! I'm curious why this wasn't caught by our Windows tests. Do we need to adjust them or add something?
cc: @elliott-with-the-longest-name-on-github

[elliott-with-the-longest-name-on-github]

I'm really not sure... I think it should be running on Windows (test-basics has instrumentation.server.ts and AFAICT it should be getting loaded by cross-platform... but I don't have a Windows machine and don't have the ability to tinker with it. I'm going to go ahead and merge this PR but also open an issue to hopefully fix this in the future.