Function compute_content_digest 

pub fn compute_content_digest(body: &[u8]) -> String

Compute the RFC 9530 Content-Digest for a message body.

Returns a structured field value in the format: sha-256=:base64:

Example

use herolib_crypt::httpsig::compute_content_digest;

let body = b"Hello, World!";
let digest = compute_content_digest(body);
assert!(digest.starts_with("sha-256=:"));
assert!(digest.ends_with(":"));