bug fix and cleanup for 0.2.16

[sonichi]

Why are these changes needed?

• await a_send
• clean up comments
• bump version to 0.2.16

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 46.61%. Comparing base (f6c9b13) to head (8e8f8a8).

Files	Patch %	Lines
autogen/agentchat/groupchat.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1827       +/-   ##
===========================================
+ Coverage   35.69%   46.61%   +10.91%     
===========================================
  Files          63       63               
  Lines        6625     6625               
  Branches     1454     1579      +125     
===========================================
+ Hits         2365     3088      +723     
+ Misses       4067     3288      -779     
- Partials      193      249       +56     

Flag	Coverage Δ
unittests	46.53% <50.00%> (+10.83%)	⬆️

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