Code tidy and improvement

[avastmick]

The original code was written quickly straight after the Gemini API was released. There are poor parts of the code:

• [ ] readability in places is poor.
• [ ] repeated code segments.
• [x] Shift impl logic into sensible module to split up the Client
• [ ] little to no test coverage.
• [ ] no CI testing.
• [ ] poor structuring.