Add scheduled builds with latest GHC

[webdevred]

This PR improves and extends our continuous integration (CI) setup with the following key updates:

• Scheduled runs: Adds a scheduled workflow (every Sunday at 05:00 UTC) to build and test the project with the latest GHC version on both Ubuntu and Windows. This complements our PR and push runs and helps catch potential issues with future GHC releases.
• Optimized cache handling: Removes the automatic cabal-update during setup to reduce redundancy, and instead runs cabal update explicitly after restoring the cache. This improves cache efficiency and minimizes unnecessary package list updates.
• Simplified .cabal file handling: Changes from a hardcoded .cabal filename to dynamically locating the .cabal file, making the CI script more generic and less error-prone when filenames change.
• Improved build and test commands: Updates cabal build and cabal test commands to include all, ensuring that all components are built and tested for more comprehensive verification.