Improved testability

[cpetersen]

This pull request does the following:

• adds rspec as a development dependency
• Removes the spec/tasks files and moves their tests into rspec
• Makes a small tweak to allow passing in a Faraday test adapter and stub so users of the library can stub network requests to it.
• Adds the ability to configure a logger
• Adds descriptions of the above features to the README.

You can test it locally with the following commands:

ollama pull phi
ollama pull yi:latest
ollama serve

# In a different terminal, in the project directory
bundle exec rspec

[cpetersen]

This is the line I needed to modify. The splat is required so I can pass in [:test, stubs] as the adapter.