restructure __internals to shave bytes; add react tests

[charkour]

This is not considered a breaking change because it relied on undocumented internal APIs that were potentially accessed in userland.

937 B --> 898 B (Saves 39 bytes)
898 B --> 871 B (Saves 27 bytes) should also improve the speed because we aren't creating new arrays (less GC)
871 B --> 862 B (Saves 9 bytes) should also improve the speed because we aren't creating new arrays (less GC)
898 B --> 880 B (saves 18 bytes) add back copying arrays to make sure reactivity stays in place
880 --> 873 B (saves 7 bytes) remove object destructuring in __handleUserSet
873 B --> 870 B (saves 3 bytes) don't spread options from user
870 B --> 868 B (saves 2 bytes) don't destructure

[charkour]

This has a bug that react won't update because the array refs won't change