Implement spotWidgetAtPosition utilities

[passsy]

This is a test if codex by OpenAI is capable of actually building stuff

Summary

• add position filter to evaluate hit tests during snapshot
• remove singular widget-at-position selector from the public API
• expose new filter in the public exports
• adjust changelog and tests for plural selector

Fixed #28

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https://chatgpt.com/codex/tasks/task_e_6850242935a48333bddbacaaf8278f60