handle moonshot

[regan-huff]

I am attempting to score an external submission for AstaBench:
https://huggingface.co/datasets/allenai/asta-bench-submissions/tree/main/1.0.0/test/EvoScientist_EvoScientist_Coder_2026-03-19_16-22-34

The solver args show this provider openrouter/moonshotai/kimi-k2.5, which comes through in the inspect model usage objects like this:

{
model: "moonshotai/kimi-k2.5-0127",
usage: {
input_tokens: 7467,
output_tokens: 829,
total_tokens: 8296,
input_tokens_cache_write: null,
input_tokens_cache_read: 6144,
reasoning_tokens: 284
}

Moonshot is supported as an inference provider in litellm and some cost objects have been added to https://github.com/BerriAI/litellm/blob/main/model_prices_and_context_window.json

However, these are not available in the version of litellm which we have chosen to pin, 1.75.8 (and in fact may not yet be in a released version). This PR adds pricing in local_cost to handle this provider/model.