Float timestamp values in RPM `repomd.xml` file

Hello,

I found some float timestamp values in the `repomd.xml` file of RPM repository (private repository handle by Cobbler).

It can be handled by using `Option` instead of `Option`.
If you are ok, I can send you a Pull Request (the update with test are already done).

Jonathan

Search the Rust code that parses RPM repository repomd.xml timestamps and inspect the existing timestamp test coverage. Confirm the float timestamp case and the proposed Option handling, then ensure the relevant tests pass with the updated behavior.

Written by the indexing model from the issue text.