Improve PURL Collection for the Rust Ecosystem

[ziadhany]

As @keshav-space suggested, collecting Cargo packages by iterating over commits and calculating diffs takes significantly more time compared to simply looping through all the files in the repo index and processing them.

The drawback, however, is that even with just a few file changes (e.g., 3), the entire workflow must be executed. In contrast, the old mechanism could detect new commits and trigger the workflow only for those.

Related pull requests:

• Add support to mine cargo Package-URLs #679