Function calculate_exact_error_identifier 

pub fn calculate_exact_error_identifier(
    service: &str,
    error_source: &str,
    message: &str,
    stack_trace: Option<&str>,
) -> String

Computes a stable BLAKE3 identifier for an exact error variant.

Framed by hash_identifier, so (“foo”, “”) and (“”, “foo”) are different variants.