Release v0.7.0

refactor: use isolated viper instances for config handling

- Replaced global `viper` usage with isolated `viper.New()` instances for better encapsulation.
- Updated `UnmarshalConfig` to accept a `*viper.Viper` instance as a parameter.
- Adjusted tests to use isolated `viper` instances.
- Improved error handling and logging for config loading and unmarshalling.