feat(watchOnce): return function for manual watcher stopping

[valerypatorius]

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⚠️ Slowing down new functions

Warning: Slowing down new functions

As the VueUse audience continues to grow, we have been inundated with an overwhelming number of feature requests and pull requests. As a result, maintaining the project has become increasingly challenging and has stretched our capacity to its limits. As such, in the near future, we may need to slow down our acceptance of new features and prioritize the stability and quality of existing functions. Please note that new features for VueUse may not be accepted at this time. If you have any new ideas, we suggest that you first incorporate them into your own codebase, iterate on them to suit your needs, and assess their generalizability. If you strongly believe that your ideas are beneficial to the community, you may submit a pull request along with your use cases, and we would be happy to review and discuss them. Thank you for your understanding.

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Description

All watchers are expected to return WatchStopHandle functions, which allow to stop these watchers manually. watchOnce was the only watcher, that could not be stopped manually. Now it can.

Additional context

Although the case, when watchOnce should be stopped manually before it'll be triggered, is rare, it is better to be consistent and provide the ability to perform cleanup.

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🤖 Generated by Copilot at bf72035

Return WatchStopHandle from watchOnce function. This allows users to stop the watcher manually and aligns the function with other watch utilities in vueuse.

🤖 Generated by Copilot at bf72035

• Return WatchStopHandle from watchOnce function to allow manual stopping and align with watch signature (link, link, link)