Before:<img width="254" alt="image" src="https://github.com/user-attachments/assets/1460ea58-c915-4c72-85c4-0655030cb99f" />After:<img width="260" alt="Screenshot 2025-05-29 at 4 41 05 pm" src="https://github.com/user-attachments/assets/34fe0293-ccc4-4686-9285-eb7482d7a10e" /> <img width="258" alt="Screenshot 2025-05-29 at 4 40 56 pm" src="https://github.com/user-attachments/assets/2bd640eb-5d11-4384-8a24-b705148c2b2a" />

Third PR for#47.Adds a script to update an existing `appcast.xml`.This will be called in CI to update the appcast before uploading it back to our feed URL (`releases.coder.com/...`). It's currently not used anywhere.Invoked like:```swift run update-appcast -i appcast.xml -s CoderDesktop.pkg.sig -v 0.5.1 -o appcast.xml -d ${{ github.event.release.body }}```To update an appcast that looks like:<details><summary>appcast.xml</summary>```xml<?xml version="1.0" encoding="utf-8" standalone="yes"?><rss xmlns:sparkle="http://www.andymatuschak.org/xml-namespaces/sparkle" version="2.0">    <channel>        <title>Coder Desktop</title>        <item>            <title>v0.5.1</title>            <description><![CDATA[<h2>What's Changed</h2><ul><li>fix: don't create http client if signed out by@ethanndickson in <a href="https://github.com/coder/coder-deskt%E2%80%A6r-desktop-macos/pull/170">https://github.com/coder/coder-deskt…r-desktop-macos/pull/170</a></li></ul><p><strong>Full Changelog</strong>: <a href="https://github.com/coder/coder-desktop-macos/compare/v0.5.0...v0.5.1">https://github.com/coder/coder-desktop-macos/compare/v0.5.0...v0.5.1</a></p>]]></description>            <pubDate>Thu, 29 May 2025 06:08:56 +0000</pubDate>            <sparkle:channel>stable</sparkle:channel>            <sparkle:version>0.5.1</sparkle:version>            <sparkle:fullReleaseNotesLink>https://github.com/coder/coder-desktop-macos/releases</sparkle:fullReleaseNotesLink>            <sparkle:minimumSystemVersion>14.0.0</sparkle:minimumSystemVersion>            <enclosure url="https://github.com/coder/coder-desktop-macos/releases/download/v0.5.1/Coder-Desktop.pkg" type="application/octet-stream" sparkle:installationType="package" sparkle:edSignature="NkyCj7Lzpw95P0N95SQHiBCjDLZYVukbRR3aOjGZAuL5Dc+I//DfTCRFCxoQNhA38uu/CCAR8v9E4SgMkDdmAA==" length="39630183"></enclosure>        </item>        <item>            <title>Preview</title>            <pubDate>Thu, 29 May 2025 06:08:08 +0000</pubDate>            <sparkle:channel>preview</sparkle:channel>            <sparkle:version>0.5.0.3</sparkle:version>            <sparkle:fullReleaseNotesLink>https://github.com/coder/coder-desktop-macos/releases</sparkle:fullReleaseNotesLink>            <sparkle:minimumSystemVersion>14.0.0</sparkle:minimumSystemVersion>            <enclosure url="https://github.com/coder/coder-desktop-macos/releases/download/preview/Coder-Desktop.pkg" type="application/octet-stream" sparkle:installationType="package" sparkle:edSignature="L0cFeyoy+D/Zgm3eXok87SKmgIUka8m2b+g7UWPReF4UhFUb4RlDsZ5PxXKd5MrtsaODGUz2iRMWraO7aQg+DA==" length="39630898"></enclosure>        </item>    </channel></rss>```</details>Producing a notification like:<img width="620" alt="image" src="https://github.com/user-attachments/assets/acae89d6-5d39-4464-bf60-7beac66af9c7" />

It's twice as fast without the cacheWith cache:<img width="296" alt="image" src="https://github.com/user-attachments/assets/865bfbaf-774d-4213-ba99-b338dbef13dd" />Without:<img width="296" alt="image" src="https://github.com/user-attachments/assets/e55be0dd-bd4e-472f-af4c-c5d06f7ef7ad" />I can only assume it's just faster to compile some of the dependencies then to copy them from the cache

Fourth PR for#47.Dry-run worked!https://releases.coder.com/coder-desktop/mac/appcast.xml

Closes#47.Stable:<img width="615" alt="image" src="https://github.com/user-attachments/assets/e34c8138-dac7-48ab-af76-0feea79c9f7e" />Preview:<img width="614" alt="image" src="https://github.com/user-attachments/assets/caeb2750-b735-473d-8568-e8f1098954d0" />Additionally:- Removes the updating of the `coder-desktop-preview` cask. - Marks the `coder-desktop` cask as auto-updating, so brew doesn't attempt to `upgrade` itself.I'll also need to make a PR on the `homebrew-coder` repo to mark it as deprecated in brew. If a user wishes to be on the preview channel, they just need to install the stable version, and switch to the preview channel in settings.