DeepSeek V4 Flash 0731 Fast

Use DeepSeek V4 Flash 0731 Fast through TrustedRouter in this project.

1. Read https://trustedrouter.com/llms.txt
2. Point the OpenAI-compatible client at
   https://api.trustedrouter.com/v1 and read the key from
   TRUSTEDROUTER_API_KEY.
3. Set the model to deepseek/deepseek-v4-flash-0731-fast.
4. Run the tests, then show me the diff before committing.

import os
from openai import OpenAI

client = OpenAI(
    base_url="https://api.trustedrouter.com/v1",
    api_key=os.environ["TRUSTEDROUTER_API_KEY"],
)
response = client.chat.completions.create(
    model="deepseek/deepseek-v4-flash-0731-fast",
    messages=[{"role": "user", "content": "What is the capital of France?"}],
)
print(response.choices[0].message.content)

curl https://api.trustedrouter.com/v1/chat/completions \
  -H "Authorization: Bearer $TRUSTEDROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "deepseek/deepseek-v4-flash-0731-fast",
    "messages": [{"role": "user", "content": "What is the capital of France?"}]
  }'