refactor: unify cache implementations

[knqyf263]

Description

Previously, fanal was a separate library, and the cache implementations for the filesystem and Redis were located within the fanal package, while the cache for server mode was implemented in the Trivy package. Now that fanal has been integrated into Trivy, there is no need to keep the cache implementations separate. As a result, we have consolidated the cache-related functionality under the pkg/cache directory.

Additionally, the S3 cache is currently not being used, causing confusion, so this PR removes it.

This refactoring aims to simplify the codebase by:

1. Unifying the cache implementations in a single package
2. Eliminating the unused and confusing S3 cache
3. Improving the overall structure and organization of the cache-related code

Checklist

• [x] I've read the guidelines for contributing to this repository.
• [x] I've followed the conventions in the PR title.
• [x] I've added tests that prove my fix is effective or that my feature works.
• [ ] I've updated the documentation with the relevant information (if needed).
• [ ] I've added usage information (if the PR introduces new options)
• [ ] I've included a "before" and "after" example to the description (if the PR is a user interface change).