Function encode_data_unsigned 

pub fn encode_data_unsigned(name: &Name, content: &[u8]) -> Bytes

Encode a Data TLV signed with DigestSha256.

Computes SHA-256(signed_region) and embeds it as the signature value. No key locator is included — DigestSha256 is self-contained integrity protection that requires no certificate or trust anchor.

FreshnessPeriod is set to 0 so management responses are never served from cache.