Add LLM rules for custom or unrecognized models

[jlowin]

Each LLM provider may have different requirements for how messages are formatted or presented. For example, OpenAI permits system messages to be interspersed between user messages, but Anthropic requires them to be at the beginning of the conversation. ControlFlow uses provider-specific rules to properly compile messages for each agent's API.

For common providers like OpenAI and Anthropic, LLM rules can be automatically inferred from the agent's model. However, you can use a custom LLMRules object to override these rules or provide rules for non-standard providers.

Here is an example of how to tell the agent to use the Anthropic compilation rules with a custom model that can't be automatically inferred:

import controlflow as cf

# note: this is just an example
llm_model = CustomAnthropicModel()

agent = cf.Agent(
    model=model,
    llm_rules=cf.llm.rules.AnthropicRules(model=model)
)