fix: enable clamp_opt for ppmd and xz

[danielrainer]

Make ppmd/xz compression work if only the respective feature is enabled.

[gemini-code-assist]

Summary of Changes

Hello @danielrainer, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a functional gap related to XZ compression. It ensures that a specific utility function, clamp_opt, is properly included in the build when the xz feature is enabled, thereby completing the necessary support for XZ compression within the system.

Highlights

• XZ Compression Support: The clamp_opt function, essential for handling compression levels, is now correctly enabled when only the xz feature is active, resolving an issue where xz compression was not fully functional under this condition.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a build issue for the xz feature by including it in the cfg attribute for the clamp_opt function. However, a similar issue exists for the ppmd feature, which also relies on clamp_opt but has been omitted from the configuration. I've provided a suggestion to include the ppmd feature to ensure its functionality when enabled in isolation.