Fall back to UIAccessibilityContainer index APIs when accessibilityElements is nil

[RoyalPineapple]

Summary

• When parsing an object whose accessibilityElements property is nil, fall back to the accessibilityElementCount() / accessibilityElement(at:) APIs before dropping through to subview traversal. This mirrors how VoiceOver resolves containers that vend elements via the dynamic UIAccessibilityContainer methods.
• A non-nil array is still honored as-is (including an empty array), matching Apple's documented semantics ("This can be used as an alternative to implementing the dynamic methods. default == nil").
• Logs a warning when a container reports more elements via accessibilityElementCount() than it actually returns from accessibilityElement(at:).

Test plan

• CI green
• Existing snapshot tests still pass

[RoyalPineapple]

🔴 Infinite-loop / CI hang: count > 0 doesn't exclude NSNotFound.

accessibilityElementCount()'s default return is undocumented in UIAccessibilityContainer.h (its siblings accessibilityElementAtIndex: → nil and indexOfAccessibilityElement: → NSNotFound are documented). On iOS 17/18/26 it returns NSNotFound (9_223_372_036_854_775_807) for objects that don't implement the dynamic container methods. That passes count > 0, so for index in 0 ..< count below runs ~9.2 quintillion iterations and hangs.

This is what's failing CI: all three Tuist Build jobs ran 6h0m and were canceled at the timeout. The iOS_18 log executes normally through testLargeView then goes silent for ~5h46m, hanging on the next test (testLargeViewInViewControllerThatRequiresTiling, a VC-hierarchy case where the parser reaches UIKit-internal non-UIView objects). (Note: on iOS 16.2 this method returns 0, so it won't reproduce on older local runtimes.)

Fix:

Suggested change

	guard count > 0 else {
	let count = accessibilityElementCount()
	guard count > 0, count != NSNotFound else {

After this, testLargeViewInViewControllerThatRequiresTiling provides regression coverage for free.

Minor (separate line): the warning below uses print(...); the rest of this file uses os_log(..., log: parserLog, type: .error, ...) (see providedContextAsSuperview). Worth matching for consistency / to avoid stdout spam in host test processes.