Migrate execution engine parsing to triad conditional_dispatcher, add dask client to DaskExecutionEngine

[goodwanghan]

No description provided.

[codecov-commenter]

Codecov Report

Merging #339 (d8595b7) into master (8cb5f7a) will not change coverage.
The diff coverage is 100.00%.

❗ Current head d8595b7 differs from pull request most recent head 5980461. Consider uploading reports for the commit 5980461 to get more accurate results

@@            Coverage Diff            @@
##            master      #339   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          100       101    +1     
  Lines         9430      9419   -11     
=========================================
- Hits          9430      9419   -11     

Impacted Files	Coverage Δ
fugue/constants.py	100.00% <ø> (ø)
fugue/execution/__init__.py	100.00% <ø> (ø)
fugue/__init__.py	100.00% <100.00%> (ø)
fugue/_utils/registry.py	100.00% <100.00%> (ø)
fugue/exceptions.py	100.00% <100.00%> (ø)
fugue/execution/factory.py	100.00% <100.00%> (ø)
fugue/registry.py	100.00% <100.00%> (ø)

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