https://github.com/ClickHouse/ClickHouse/blob/9a48cf0da8badfc5f3da08611eb44961aa28e3f6/src/Functions/FunctionsHashing.h#L669-L671

There's a call to `blake3_free_char_pointer` that passes ownership of the pointer back to Rust (which then frees the memory), then there's a call to `std::string`'s constructor that accepts that now-freed pointer.
{
        union
        {
            unsigned char char_data[16];
            uint64_t uint64_data;
        } buf;
        MD5_CTX ctx;
        MD5_Init(&ctx);
        MD5_Update(&ctx, reinterpret_cast<const unsigned char *>(begin), size);
        MD5_Final(buf.char_data, &ctx);
        return Poco::ByteOrder::flipBytes(static_cast<Poco::UInt64>(buf.uint64_data));        
    }
    static UInt64 combineHashes(UInt64 h1, UInt64 h2)
    {
        UInt64 hashes[] = {h1, h2};
        return apply(reinterpret_cast<const char *>(hashes), 16);
    }
    
    
    static constexpr bool use_int_hash_for_pods = false;
};
struct MD4Impl
{
    static constexpr auto name = "MD4";
    enum { length = MD4_DIGEST_LENGTH };