[WIRES] Make plugin compatible with wires refactor

[mariaschuld]

This PR updates the plugin to support the new wire management in PennyLane master.

[codecov]

Codecov Report

Merging #37 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #37   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          222       224    +2     
=========================================
+ Hits           222       224    +2     

Impacted Files	Coverage Δ
pennylane_cirq/cirq_device.py	100.00% <100.00%> (ø)

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[mariaschuld]

In future it would be also nice to be a bit cleverer about how to support cirq's GridQubits and LineQubits...But this is a minimal version against the breaking changes!

[josh146]

Nice, looks like the changes were very minor!

[thisac]

Looks good @mariaschuld! 🎉

[thisac]

Oh, so if I understand this correctly, self.map_wires will in this case go from e.g. self.wires -> ['q1', 'ancilla', 0, 1] to device_wires -> [0, 1, 2, 3]. And then the list of wires can be extracted from the Wires object with device_wires.labels. Is this correct?

[mariaschuld]

Yes, perfect! Well, strictly speaking the map goes from self.wires -> Wires(['q1', 'ancilla', 0, 1]) to device_wires -> Wires([0, 1, 2, 3]), and device_wires.labels is the tuple (0, 1, 2, 3)...