[Zellic] 7 Circuit framework allows overwriting wires

[manishbista28]

The circuit crate defines traits and utilities for defining Boolean circuits for use in garbling.
ExecuteMode is defines with the following method:

#[inline]
    fn feed_wire(&mut self, wire_id: WireId, value: Self::WireValue) {
        if matches!(wire_id, TRUE_WIRE | FALSE_WIRE | WireId::UNREACHABLE) {
            return;
        }

        self.storage
            .set(wire_id, |entry| *entry = Some(value))
            .unwrap();
    }

The value in storage corresponding to a given wire ID is Some or None depending on if it has been
already set. This method directly sets the value of a gate's output wire in storage, without checking
if it has been already set. But it should not be possible for gates to share output wires; otherwise,
the gate that gets evaluated second would overwrite the output of the first one. So feed_wire
should check if the entry being written to is Some or None and panic if it is Some already