Get usage summary

curl --request GET \
  --url https://runcrate.ai/api/v1/billing/usage \
  --header 'Authorization: Bearer <token>'

{
  "data": {
    "total_requests": 123,
    "total_prompt_tokens": 123,
    "total_completion_tokens": 123,
    "total_tokens": 123,
    "total_cost": 123
  }
}