Fix xy angle sign

[YonatanGideoni]

What

This PR fixes the wrong sign that was used for the xy_angle in the phase in the Instruction class.

Why

Makes rotations on the bloch sphere be in the correct direction. Closes #231

How

Removed minus sign.

Remarks

None

Checklist

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• Notebooks - Example notebooks have been updated to incorporate changes and new features
• Changelog - A short note on this PR has been added to the Upcoming Release section

[YonatanGideoni]

The cases where the tests are failing seem to be because of fairly small differences in the resulting optimal parameters for various optimisations/calibrations (except for maybe test_flux_signal, where the differences are on the order of ~10%). What should I do to deal with this? Create new parameter files? @lazyoracle

[lazyoracle]

The cases where the tests are failing seem to be because of fairly small differences in the resulting optimal parameters for various optimisations/calibrations (except for maybe test_flux_signal, where the differences are on the order of ~10%). What should I do to deal with this? Create new parameter files? @lazyoracle

In general, failing tests should not be modified to get them to pass. Do you possibly have some insight on why the optimal parameters changed? If however the change in the test optimal parameters is expected as a result of the code change in the PR, then feel free to just modify the parameters and move on. Make sure to note in your commit message the reasoning behind why the test was modified.

[nwittler]

With optimization results, it can be tricky when the convention changed. An alternative to what Anurag suggested would be to change the gate definitions in those tests from phase -> -phase to recreate the previous behavior. Then add a note that the convention here goes the "wrong" way.
If this does not work, something else is wrong.

[nwittler]

Looks good and can be approved when the discussed problems are resolved.

[codecov]

Codecov Report

Merging #232 (6cb0563) into dev (76bdf7b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #232   +/-   ##
=======================================
  Coverage   74.82%   74.82%           
=======================================
  Files          38       38           
  Lines        5534     5534           
=======================================
  Hits         4141     4141           
  Misses       1393     1393           

Impacted Files	Coverage Δ
c3/signal/gates.py	95.02% <100.00%> (ø)

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