fix(types): add shipping address change errors

[jdjioe5-cpu]

Summary

Fixes #824 by updating the onShippingAddressChange button callback types to match the documented JavaScript SDK shape:

• adds data.errors with the documented shipping address error keys
• updates actions.reject to accept an error message string
• adds a type test that rejects unsupported countries with data.errors.COUNTRY_ERROR

PayPal docs reference: https://developer.paypal.com/docs/regional/th/checkout/reference/customize-sdk/#onshippingaddresschange

Validation

npx prettier --check packages/paypal-js/types/components/buttons.d.ts packages/paypal-js/types/tests/buttons.test.ts
npm run typecheck --workspace=@paypal/paypal-js
npm run lint --workspace=@paypal/paypal-js
git diff --check

[changeset-bot]

🦋 Changeset detected

Latest commit: f1268fe

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

This PR includes changesets to release 1 package

Name	Type
@paypal/paypal-js	Patch

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