Use list for GoogleNoiseProperties.readout_errors values

[pavoljuhas]

Problem: The values in SuperconductingQubitsNoiseProperties.readout_errors
and GoogleNoiseProperties.readout_errors dictionaries are declared as
np.ndarray in docstrings, but annotated aslist[float] in the code,
and can be set to either type. JSON serialization fails when assigned a list.

Solution: Always convert to list[float] following the type annotation.

This fixes serialization failure for GoogleNoiseProperties objects created
with noise_properties_from_calibration.

[pavoljuhas]

Question @dstrain115 - The json_test_data/GoogleNoiseProperties.repr file expresses readout_errors as np.array-s:

Cirq/cirq-google/cirq_google/json_test_data/GoogleNoiseProperties.repr

Lines 21 to 25 in 09b44c0

	readout_errors={
	cirq.GridQubit(0, 0): np.array([0.004, 0.007], dtype=np.float64),
	cirq.GridQubit(0, 1): np.array([0.005, 0.008], dtype=np.float64),
	cirq.GridQubit(1, 0): np.array([0.006, 0.009], dtype=np.float64)
	},

This passes tests because GoogleNoiseProperties.__eq__ uses np.allclose to compare readout_errors values.

Should we leave it as is or is it better to update GoogleNoiseProperties.repr?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.68%. Comparing base (123cbf8) to head (e735a43).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7392      +/-   ##
==========================================
- Coverage   98.68%   98.68%   -0.01%     
==========================================
  Files        1112     1112              
  Lines       97737    97755      +18     
==========================================
+ Hits        96454    96471      +17     
- Misses       1283     1284       +1     

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