Function recompute_entry_hash 

pub fn recompute_entry_hash(
    entry_id: &str,
    store: &str,
    key: &str,
    capability_id: &str,
    receipt_id: &str,
    written_at: u64,
    prev_hash: &str,
) -> Result<String, MemoryProvenanceError>

Compute the canonical hash that binds every field of an entry into the chain.

Separated from MemoryProvenanceEntry::expected_hash so SQLite impls can call it before they have constructed the full entry.