Fix install and update on devices that include unzip

[nchapman]

No description provided.

[Copilot]

Pull request overview

This pull request enhances the atomic update system to handle platforms that bundle their own unzip binary while maintaining compatibility with platforms that rely on the system's unzip command. The changes also improve error handling by implementing comprehensive backup restoration logic when updates fail.

Key Changes

• Dynamic unzip binary selection: Detects and uses platform-bundled ./unzip when available, falling back to system unzip otherwise
• Improved error handling: Restructured success/failure paths with automatic restoration of both .system and .tmp_update directories from backups when unzip fails
• Consistent naming: Changed backup suffix from -old to -prev for uniformity across both .system and .tmp_update backups

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