Function cache_write_multiplier 

pub fn cache_write_multiplier(model: &str) -> f64

Multiplier applied to input_price for cache-write tokens. Only Anthropic/Bedrock bill a surcharge for cache writes (1.25×). For providers that cache implicitly (OpenAI, Gemini, GLM) this is 0.0 because the write is bundled into the regular input price.