Refactor of flow tools - OpenGraph.compose

[matulni]

This commit adapts the existing method :func: OpenGraph.compose to the new API introduced in #358.

Note that tests use the comparison utilities introduced in #374. To ease the review, this is a pull request on the TeamGraphix:rf_og_compare branch.

[codecov]

Codecov Report

❌ Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.32%. Comparing base (55abf0a) to head (fe40a74).
⚠️ Report is 2 commits behind head on rf_og_compare.

Files with missing lines	Patch %	Lines
graphix/random_objects.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##           rf_og_compare     #375      +/-   ##
=================================================
+ Coverage          86.25%   86.32%   +0.07%     
=================================================
  Files                 44       44              
  Lines               6163     6166       +3     
=================================================
+ Hits                5316     5323       +7     
+ Misses               847      843       -4     

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