refactor model class and runners to be more independent

[deigen]

Currently, the ModelRunner is the primary object of instantiation for a model in a server. This has several drawbacks:

• The user can't directly create their model without also creating a Runner, unless always including boilerplate workarounds. Creating a model directly is useful for testing and local use.
• It's cumbersome to create gRPC-served models, as they also require instantating a Runner class.
• The instantiation process of the Model in the server isn't clear, at no point is there a straightforward call to model = Model(**args); the init is instead the Runner init.

Instead, we should define the model implementation using ModelClass directly, and create Runner and gRPC servers that can each call the Model object. This separates the model class from the server method, while still maintaining the same interfaces.

NOTE: This change also requires us to change the base class of all models in the examples repo, to use ModelClass instead of ModelRunner as their base class.

[github-actions]

Package	Line Rate	Health
clarifai	43%	❌
clarifai.cli	65%	➖
clarifai.client	71%	➖
clarifai.client.auth	74%	➖
clarifai.constants	100%	✔
clarifai.datasets	100%	✔
clarifai.datasets.export	80%	✔
clarifai.datasets.upload	75%	➖
clarifai.datasets.upload.loaders	37%	❌
clarifai.models	100%	✔
clarifai.modules	0%	❌
clarifai.rag	72%	➖
clarifai.runners	12%	❌
clarifai.runners.models	57%	➖
clarifai.runners.utils	66%	➖
clarifai.schema	100%	✔
clarifai.urls	80%	✔
clarifai.utils	77%	➖
clarifai.utils.evaluation	67%	➖
clarifai.workflows	94%	✔
Summary	68% (4411 / 6526)	➖

Minimum allowed line rate is 50%