Remove Async keyword from PayPalNativeCheckoutClient.start function and fix tests

[KunJeongPark]

Summary of changes

• Remove async from PayPalNativeCheckoutClient.start function since the results are returned via delegate methods.
• Checked with Project build setting Strict Concurrency Checking option set to complete for this change, no warnings, errors found. There are warnings and compile errors in other modules separate from this PR, so I made another ticket to address them.

-Reverted above changes with comment to remove Async for next major version.

Checklist

~- [ ] Added a changelog entry~

Authors

• @KunJeongPark @sshropshire

[scannillo]

Our repo docs also need to be updated for this change, and our dev docs as well

[KunJeongPark]

Our repo docs also need to be updated for this change, and our dev docs as well

Do we keep the documentation for deprecated functions here and in the dev docs? The dev docs needs to be another ticket, different repo. I'll hold on dev docs change until we agree on the new function name

[scannillo]

Do we keep the documentation for deprecated functions here and in the dev docs?

Great question. If a function is deprecated in our SDK, our docs should not be using it. The docs should be updated to showcase the newest, suggested way of integrating.

The dev docs needs to be another ticket, different repo. I'll hold on dev docs change until we agree on the new function name

Agreed! Dev docs is another repo, so a separate ticket is a great call