Anthropic Prompt Caching and more

[biobootloader]

Add support for Anthropic prompt caching. See scripts/caching.py for usage

Other things:

• SpiceMessage is no longer just openai.ChatCompletionMessageParam
• lots of things switched to pydantic
• we now don't auto-convert as much to force things to work with Anthropic - we error instead
• message chaining / get a messages object from client:

messages = (
    client.new_messages()
    .add_system_message("You are a helpful assistant.")
    .add_user_message("list 5 random species of birds")
)

[granawkins]

LGTM. I like the update to pydantic models and using .attr instead of ['attr'], and adding cache as a message input seems convenient.