Ignore undefined style values on native

[adityasingh2400]

Fixes #452

On native, returning undefined for a property from an inline style function (or any style object with an undefined value) leaks that key through processStyle and into the style resolver, which throws styleq: <cssAtom> typeof undefined is not "string" or "null". This is a regression; these values used to be dropped, and on web undefined values are simply ignored.

The loop in processStyle branches on object/string/number, so an undefined value falls through to the catch-all assignment and ends up in the result as { rowGap: undefined }. This adds an early continue for undefined values so the property is omitted, matching web behavior and letting inline style functions return undefined to opt out of a property.

null is left untouched since the resolver accepts it.

Testing: added a regression test under css.create() > values: general that asserts the property is absent when the inline function returns undefined. Confirmed it fails on main and passes with the fix. Full native + web jest suites pass (888 tests, 711 snapshots unchanged), Flow and ESLint clean.

[MoOx]

Any reason you closed this ?

[adityasingh2400]

Sorry @MoOx, no reason related to the change itself. I closed it by accident while bulk cleaning up stale forks on my profile, and since the fork got deleted I could not reopen this one directly. I have restored the exact same branch and opened #498 to continue it. Happy to address review feedback there.