feat: focusedValue, and worklet focus handlers that see autoFocus

[ronickg]

Why

Uno wants every input to show a blue border the moment it's focused, around the whole field row: a leading icon or country picker, the field itself and a trailing clear button. NitroInput's own frame (variant) only wraps the NitroInput view, and native views can't hold children. The other option, JS onFocus plus setState, costs a JS round trip before the border shows.

A glitch sweep in Uno also turned up an iOS keyboard bug, fixed in the same release (see the last item under What).

What

• focusedValue prop: pass a shared value (useSharedValue(false)). The field sets it on the UI thread the moment focus changes, and onFocus / onBlur keep running on JS. The app then draws the border on its own row from the shared value, in the same frame the caret appears.
• Focus worklets now register while rendering: previously they registered in an effect, so an autoFocus field's first focus could arrive before registration and be dropped. This also fixes worklet onFocus and useNitroInputState().focused for autoFocus fields.
• iOS: no keyboard left over a screen popped back to. Going back from a screen whose focused field has keyboardHandoffMs, to a screen where no field takes the keyboard (Uno's account list after the amount screen), the keyboard stayed up over that screen for the whole hold.
  • Cause: React unmounts the popped screen's field before react-native-screens starts the pop, so at the handoff a pop looks exactly like a field swapped in place.
  • Fix: a hold now watches the leaving field's screen. When that screen starts to leave (react-native-screens takes it out of its navigation controller), the hold ends, unless a field is waiting for the keyboard (a covered field taking it back, or a focus() held for its view).
  • Result in Uno: the keyboard now slides out with the popped screen. Pops back to a field that had the keyboard still keep it.

Tests

• bun run test: 171/171. The README and docs props tables are updated.
• bun run typecheck
• bun run test:harness:ios: 120/120. Two new keyboard tests: the keyboard goes after a pop to a screen whose field does not take it (it failed before the fix, with a 3 s hold), and it stays for a covered field that takes it back. The Harness can't load worklets, so focusedValue itself was checked in Uno (below).
• In Uno, on the iPhone 17 simulator:
  • the autoFocus field shows the border on first focus;
  • moving focus between the three name fields switches the border in the same frame as the caret;
  • the phone field's border wraps the flag and country code;
  • recordings of amount → back (the keyboard leaves with the screen) and phone → back to the text step (the keyboard stays and changes type in place).
• Android: no native change.

Release as 0.3.5 (the changelog heading is already ## 0.3.5).

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