chore: import upstream snapshot with attribution

examples/cache-usage/README.md

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+# WebLLM Cache Usage
+
+WebLLM supports multiple persistent cache backends. You can pick the classic Cache API, IndexedDB, [Origin Private File System (OPFS)](https://developer.mozilla.org/en-US/docs/Web/API/File_System_API/Origin_private_file_system), or the experimental Chrome [Cross-Origin Storage](https://github.com/WICG/cross-origin-storage) extension by
+setting `AppConfig.cacheBackend` to `"cache"`, `"indexeddb"`, `"opfs"`, or `"cross-origin"`.
+This folder provides an example on how different caches are used in WebLLM. We also
+demonstrate the utility cache functions such as deleting models, checking if models are in cache, etc.
+
+> **Note:** The cross-origin backend requires installation of the [Cross-Origin Storage browser extension](https://chromewebstore.google.com/detail/cross-origin-storage/denpnpcgjgikjpoglpjefakmdcbmlgih) ([source code](https://github.com/web-ai-community/cross-origin-storage-extension)). This does not currently support programmatic tensor-cache deletion; deletion is extension-managed.
+
+> **Note:** If `"opfs"` is selected in an environment without OPFS support, cache operations fail with an OPFS availability error.
+> Use `appConfig.opfsAccessMode = "auto"` to use OPFS sync access handles where supported, or `"sync"` to require sync access handles. The default is `"async"`.
+
+For more information about Cache API and IndexedDB, see:
+https://developer.mozilla.org/en-US/docs/Web/API/Storage_API/Storage_quotas_and_eviction_criteria#what_technologies_store_data_in_the_browser.
+
+To inspect the downloaded artifacts in your browser, open up developer console, go to application,
+and you will find the artifacts under `IndexedDB`, `Cache storage`, or OPFS (under the browser's origin-private file system). When `"cross-origin"` is selected,
+the extension displays origins and resource hashes.
+
+To run the example, you can do the following steps under this folder
+
+```bash
+npm install
+npm start
+```
+
+Note if you would like to hack WebLLM core package.
+You can change web-llm dependencies as `"file:../.."`, and follow the build from source
+instruction in the project to build webllm locally. This option is only recommended
+if you would like to hack WebLLM core package.