Refactors: Driver to Provider + misc updates

[sixlive]

Description

Drivers to Providers

Closes #19

• Removes the concept of 'drivers' and now just uses providers.
• Creates Ollama provider since it was previously using the OpenAI driver

Manager Resolution

Updates the provider manager to allow for resolution using the, new, Provider enum.

Prism::text()
    ->using('anthropic', 'claude-3-5-sonnet-20240620')
    ->prompt('introduce yourself')
    ->generate();
    
use EchoLabs\Prism\Enums\Provider;

Prism::text()
    ->using(Provider::Anthropic,  'claude-3-5-sonnet-20240620')
    ->prompt('introduce yourself')
    ->generate();

Misc refactors

• Add the generate method in addition to __invoke for better readability