Rethink exported types in sdk-starter-kit

[yagopv]

Context

The extend() method in the sdk-starter-kit does not work well with typing across different files where the extend variable is not defined. Currently, we only export a SafeClient type, which complicates the use of extensions in the projects using the kit.

For example, we had to implement a special SafeClient in the safe-react-hooks to resolve TypeScript errors.

Proposed solution

Export the main types from the sdk-starter-kit, such as a SafeOperationsClient type, that can be used in other projects without needing to define it explicitly.