sfixed64(value) {
        let chunk = new Uint8Array(8);
        let view = new DataView(chunk.buffer);
        let long = pb_long_1.PbLong.from(value);
        view.setInt32(0, long.lo, true);
        view.setInt32(4, long.hi, true);
        return this.raw(chunk);
    }
Write a `fixed64` value, a signed, fixed-length 64-bit integer.