perf(react-form): skip updating isValidating by default

[MVaik]

fixes https://github.com/TanStack/form/issues/1130

BREAKING CHANGE: isValidating is now opt-in

[MVaik]

Unsure if this is even the right direction, as it's essentially flipping an established default purely for react performance. Alternative could be to make disabling it opt-in instead? Would mean adding the option to every React field if you care to.

[crutchcorn]

We absolutely cannot (and should not) force an API shift simply for minor perf gains.

However, we can check if this field is read by using a proxy if that's a route we want to investigate.

Closing this PR on that principal.

Side note; I'm like 99% sure this can be fixed simply by adding a batch method call from TanStack Store somewhere... I just dunno where at a quick glance. Your test will help figure this out - keep digging! 😄🤘