add typing to aiokafka/coordinator/*

[dimastbk]

Changes

Fixes #

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[ods]

(offtopic) Why is it class method? It's strange to have a shared state among all clients

[codecov]

Codecov Report

Attention: Patch coverage is 96.06987% with 9 lines in your changes missing coverage. Please review.

Project coverage is 95.02%. Comparing base (14aa358) to head (5bf26b2).

Files	Patch %	Lines
...ka/coordinator/assignors/sticky/sticky_assignor.py	93.75%	3 Missing and 2 partials ⚠️
...iokafka/coordinator/assignors/sticky/sorted_set.py	85.00%	1 Missing and 2 partials ⚠️
aiokafka/coordinator/assignors/roundrobin.py	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1006      +/-   ##
==========================================
- Coverage   95.04%   95.02%   -0.03%     
==========================================
  Files         114      114              
  Lines       16906    16970      +64     
  Branches     2759     2771      +12     
==========================================
+ Hits        16068    16125      +57     
- Misses        493      497       +4     
- Partials      345      348       +3     

Flag	Coverage Δ
cext	91.94% <96.06%> (+<0.01%)	⬆️
integration	94.67% <96.06%> (-0.03%)	⬇️
purepy	94.45% <96.06%> (-0.06%)	⬇️
unit	52.86% <96.06%> (+0.14%)	⬆️

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