Refactor error handling to use thiserror exclusively (remove anyhow)

[7h3cyb3rm0nk]

The codebase currently uses both anyhow and thiserror for error handling. While anyhow is convenient for applications, thiserror provides better type safety, explicit error variants, and improved maintainability.

consider:

• Refactoring all anyhow usage to thiserror.
• Defining custom error types derived via thiserror in relevant modules