Count Anthropic Tokens

Body for /v1/messages/count_tokens, same fields as messages but max_tokens is optional.

Not a pass-through body: count_tokens_for_request runs litellm's tokenizer locally and never builds a provider call, so there is nothing for an unknown field to reach. Unknown fields are dropped rather than refused, which also keeps tags working here: this body does not inherit TagsBody, and litellm happens to reserve that name.

Response body for POST /v1/messages/count_tokens.