Function fetch_usage 

pub async fn fetch_usage(
    client: &UsageClient,
    provider: OAuthProviderId,
    account_label: &str,
    access_token: &str,
    opts: &UsageFetchOptions,
) -> Result<UsageSnapshot, UsageError>

Read-only usage fetch for one (provider, account) using the caller’s already-resolved access token. See the module docs for the guarantees.