iOS imperative page commands accept negative and out-of-range indices

[OskarEichler]

At master 7926b28, PagerViewProvider.goTo assigns any index to the SwiftUI selection. Android already ignores commands outside its page range. A source-based UIKit Simulator harness shows setPage(-1) and setPage(pageCount) overwrite a valid selection. Proposed fix: ignore indices outside props.children.indices for both animated/nonanimated commands, without changing the initialPage property path or the modal-animation work in PR #1102. This source audit is AI-assisted.