Fix record changed() logic for comparing current value Dates

[jcao49]

We are currently not calculating record.changed correctly for datetime fields as we compare the current value as a Date instance against the previous value which is stored as a string. We need to make sure that in any case where the current/previous is being compared as a Date vs string we convert the string to a Date and compare the actual dates based on that.

@pistachiobaby if you can pls 🎩 :) :
To see the problem:

1. In production, create a shopify app and add a real connection. Select the Product model
2. In product update action in the run function, add (before the await save(record) call)

if (record.changed("publishedAt")) {
    logger.info(`in my run function publishedAt was updated to: ${record.publishedAt}`);
}

Add the same snippet in the onSuccess function

if (record.changed("publishedAt")) {
    logger.info(`in my onSuccess function publishedAt was updated to: ${record.publishedAt}`);
}

3. Trigger a product/update webhook to create the product record with the create action. Trigger the webhook again to actually run the update action
4. See that the record.changed("publishedAt") condition was false in the run function and no log in it is shown
5. See that the record.changed("publishedAt") condition was true in the onSuccess function and the log in it is shown even though the publishedAt didn't actually change! <--- this is the bug

To see the fix:

1. cd into /packages/api-client-core
2. Run pnpm build and then pnpm pack to generate the tarball
3. Stop dev if its currently running the main gadget repo
4. In the main gadget repo, in the root package.json set the @gadgetinc/api-client-core package to point to the newly generated tarball

"@gadgetinc/api-client-core": "file:/Users/jennycao/dev/js-clients/packages/api-client-core/gadgetinc-api-client-core-0.15.36.tgz",

Do the same in UserlandDependencyVersions.ts
9. Run pnpm install
10. run dev again
11. Follow the same steps as before but this time see that record.changed("publishedAt") is correctly false in the onSuccess function

PR Checklist

• Important or complicated code is tested
• Any user facing changes are documented in the Gadget-side changelog
• Any immediate changes are slated for release in Gadget via a generated package dependency bump
• Versions within this monorepo are matching and there's a valid upgrade path

[jasong689]

changes look good. will 🎩

[pistachiobaby]

🎩 ✅

Published Product Update webhook no longer incorrectly returns true for `record.changed("publishedAt") ✅

Unpublished -> Published product does return true for both scenarios ✅