refactor: Fix React Compiler hint in CheckboxField

[frankieyan]

Part of #1066.

• File: src/checkbox-field/checkbox-field.tsx
• Violation: Support destructuring of context variables (Hint, line 66): the prop destructuring in the forwardRef render function.

Steps

1. Reproduce and confirm. Hint severity, but the component is still not memoized (confirmed in the compiled output).
2. Fix per #mutating-props (the prop reassignment of indeterminate on line 73 is the underlying mutation).
3. Confirm the count dropped; let the hook update the record file.
4. Verify memoization in the compiled output.