Function assert_hearsay_belief 

pub fn assert_hearsay_belief(
    agent_did: u64,
    proposition_hash: u64,
    informant_did: u64,
    ts: u64,
) -> [NQuin; 3]

Record that agent_did holds a HearsayBelief about proposition_hash, received from informant_did (an unverified peer).

Returns 3 quins in agent_epistemic_context(agent_did):

1. agent_did → believesViaHearsay → proposition_hash
2. agent_did → cog:believes → proposition_hash
3. proposition_hash → prov:wasDerivedFrom → informant_did (hearsay source)