Fix timestamp in compress.

[JSeimizu]

What's changed

When executing compound and collection compression, timestamp has been added twice for both tar and second compression. This PR remove the timestamp for the second compression.

Fixes #11

[saimizi]

Summary

This PR fixes issue #11 by preventing duplicate timestamps in compound compression operations. The solution correctly disables the timestamp for the secondary compression step, ensuring timestamps only appear once in the final filename.

What works well:

• The fix correctly addresses the root cause by setting TimestampOption::None for the secondary compression
• Both compound.rs and collection.rs are updated consistently
• The approach properly uses the builder pattern with with_timestamp() method
• Changes are minimal and focused on the specific issue

Minor issue:

• There's an incorrect comment in collection.rs line 121 that says "Preserve timestamp option" when it should say something like "Disable timestamp for secondary compression" (see inline comment)

Recommendation:

Approve with minor comment fix requested. The code logic is correct and solves the problem. Only the misleading comment needs to be corrected for clarity.