Added no regression tests for persistence

[LanderOtto]

This PR adds some no regression tests on the persistence module and fixes some save and load methods

[codecov-commenter]

Codecov Report

Base: 63.25% // Head: 65.32% // Increases project coverage by +2.07% 🎉

Coverage data is based on head (94b48ff) compared to base (4055469).
Patch coverage: 100.00% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #56      +/-   ##
==========================================
+ Coverage   63.25%   65.32%   +2.07%     
==========================================
  Files          73       73              
  Lines        8596     8631      +35     
  Branches     2037     2048      +11     
==========================================
+ Hits         5437     5638     +201     
+ Misses       2803     2633     -170     
- Partials      356      360       +4     

Impacted Files	Coverage Δ
streamflow/cwl/transformer.py	79.86% <ø> (+4.16%)	⬆️
streamflow/main.py	35.66% <ø> (ø)
streamflow/core/deployment.py	92.23% <100.00%> (+11.18%)	⬆️
streamflow/core/workflow.py	91.55% <100.00%> (+15.49%)	⬆️
streamflow/cwl/step.py	91.62% <100.00%> (+0.16%)	⬆️
streamflow/workflow/step.py	80.13% <100.00%> (+4.58%)	⬆️
streamflow/workflow/token.py	93.33% <100.00%> (+9.33%)	⬆️
streamflow/data/aiotarstream.py	37.94% <0.00%> (+0.12%)	⬆️
streamflow/cwl/utils.py	86.72% <0.00%> (+0.27%)	⬆️
streamflow/workflow/combinator.py	89.34% <0.00%> (+0.81%)	⬆️
... and 11 more

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