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

[MVaik]

fixes #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.

[MVaik]

"should properly update conditionally rendered fields" is now failing after this change, the "hello" that is written into firstField somehow ends up in secondField after the checkbox is toggled and firstField is no longer shown. This turns secondField into "helloworld" instead of "world".

[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! 😄🤘