Function request_id 

pub fn request_id(
    url: &str,
    method: &str,
    body: &[u8],
    format: UrlResponseFormat,
    schema_id: Option<[u8; 32]>,
) -> [u8; 32]

Canonical identifier for an oracle request. Derived deterministically from (url, method, body) - same request across validators yields the same request_id with no coordination needed.