Add conversion between qcodes legacy DataSet and xarray format

[peendebak]

Changes proposed in this pull request:

• Add conversion methods between the QCoDeS legacy dataset and xarray Dataset

A minimal example:

from qcodes.tests.legacy.data_mocks import DataSet1D, DataSet2D
qd = DataSet1D()
xds = qd.to_xarray()  
print(xds)
qds = DataSet.from_xarray(xds)

@jenshnielsen The goal of this PR is to allow conversion between the easy cases (e.g. 1D, 2D). Since the two datasets have slightly different formats, we do not cover all cases. Can you comment on whether this functionality can be added to qcodes and if the structure of the PR is good?

[codecov]

Codecov Report

Merging #2938 (12fa5a7) into master (be6ed96) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2938      +/-   ##
==========================================
+ Coverage   65.31%   65.41%   +0.10%     
==========================================
  Files         209      209              
  Lines       28037    28122      +85     
==========================================
+ Hits        18312    18397      +85     
  Misses       9725     9725              

[jenshnielsen]

@peendebak Thanks, I will have a look. Happy to merge this to QCoDeS. I have edited the description to clarify that this is about the legacy data.dataset and not the current QCoDeS dataset.

[astafan8]

@peendebak thanks for the contribution (and the typing, and the tests)! if this helps for the users of the legacy DataSet, let's get it in :)

[peendebak]

@astafan8 I addressed the comments, and added some more tests. The build seems to be failing due to a general error.

[astafan8]

The build seems to be failing due to a general error.

@peendebak what do you mean with "general error"? the error here https://github.com/QCoDeS/Qcodes/pull/2938/checks?check_run_id=2399670141 seems to be a typo in the assert method call:

>       self.asserEqual(qd.default_parameter_array().shape, xarray_dataset.tmin.shape)
E       AttributeError: 'TestDataSet' object has no attribute 'asserEqual'

it should be assertEqual, with "t" :)