adding description to State, some cleaning

[djarecka]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Summary

• adding description to State,
• renaming auxiliary
• some cleaning, removing functions that are not used anymore

Checklist

• All tests passing
• I have added tests to cover my changes
• I have updated documentation (if necessary)
• My code follows the code style of this project
  (we are using black: you can pip install pre-commit,
  run pre-commit install in the pydra directory
  and black will be run automatically with each commit)

Acknowledgment

• I acknowledge that this contribution will be available under the Apache 2 license.

[codecov]

Codecov Report

Merging #136 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #136      +/-   ##
==========================================
+ Coverage    87.1%   87.23%   +0.12%     
==========================================
  Files          16       16              
  Lines        2358     2193     -165     
  Branches      583      528      -55     
==========================================
- Hits         2054     1913     -141     
+ Misses        208      194      -14     
+ Partials       96       86      -10

Flag	Coverage Δ
#unittests	87.23% <100%> (+0.12%)	⬆️

Impacted Files	Coverage Δ
pydra/engine/core.py	87.56% <100%> (-0.07%)	⬇️
pydra/engine/helpers_state.py	91.06% <100%> (ø)
pydra/engine/state.py	94.93% <100%> (-0.03%)	⬇️

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[mgxd]

Sorry for the late review here:

@djarecka any reason for separating helpers into their own file instead of including them in state.py?
Not necessarily as part of the State class, but within the same file.

[djarecka]

nothing special, the same reason way we have other files with helping functions.