Promote unit of parameter to be a property

[jenshnielsen]

Inspired by the typing hacks needed in #3916 to make unit a property

This eliminates the need for those hacks See https://github.com/QCoDeS/Qcodes/pull/3916/files#diff-5478d126afe3357045220d8be1ef9c6859ee8427f28984ff8d169b9ab1b75902R126

• Should we do this for other _BaseParameter subclasses. No need

[codecov]

Codecov Report

Merging #3929 (1fe6b12) into master (cb7fbde) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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##           master    #3929   +/-   ##
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  Coverage   66.07%   66.07%           
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  Files         228      228           
  Lines       31153    31160    +7     
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+ Hits        20583    20590    +7     
  Misses      10570    10570           

[astafan8]

making a property is nice, but if it's only about typing, would annotating the unit attribute in __init__ where it's defined suffice?

about adding unit property to _BaseParameter - i don't think it's particularly useful since most of the "useful" parmaeters inherit from Parameter, and the only two that inherit from _BaseParameter are Array and Multi parameter , where the first one is sort of deprecated and the latter one has concept of units with s as opposed to unit.

[jenshnielsen]

making a property is nice, but if it's only about typing, would annotating the unit attribute in init where it's defined suffice?

The reason for doing this it to allow a subclass to do the same without having to ignore type checking errors. See https://github.com/QCoDeS/Qcodes/pull/3916/files#diff-5478d126afe3357045220d8be1ef9c6859ee8427f28984ff8d169b9ab1b75902R126