feat(models): allow SystemContentBlocks in LiteLLMModel

[dbschmigelski]

Description

This is the followup to feat(models): add SystemContentBlock support for provider-agnostic caching #1112. We are now processing SystemContentBlocks within LiteLLM which enables prompt caching.

Note, this will be breaking for some integrators. At launch, it was a mistake to not apply kwargs to all public methods. This leaves us with two options.

1. Forever maintain these with branching logic
2. Make a one time breaking change to apply kwargs everywhere

For the sake of maintainability, and the expectation that very few people will be extending the OpenAIModel as a base model, the proposal in this PR is to add kwargs to the existing public methods. This will enable future changes in a backwards compatible way.

Related Issues

#937

Documentation PR

To come after the merge.

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• [todo] I have updated the documentation accordingly
• [todo] I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[codecov]

Codecov Report

❌ Patch coverage is 90.74074% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/strands/models/litellm.py	85.71%	0 Missing and 5 partials ⚠️

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