Enhanced Independent Coverage Reporting

[IANTHEREAL]

Why are these changes needed?

Reference #857 (comment) discussion on CI failure

Each test may require different dependencies, so they need to be run separately. And each job needs to upload the coverage report in the same way.

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

All modified and coverable lines are covered by tests ✅

Comparison is base (31c1664) 25.24% compared to head (4bd5db2) 38.09%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #886       +/-   ##
===========================================
+ Coverage   25.24%   38.09%   +12.84%     
===========================================
  Files          28       28               
  Lines        3728     3728               
  Branches      848      890       +42     
===========================================
+ Hits          941     1420      +479     
+ Misses       2710     2180      -530     
- Partials       77      128       +51     

Flag	Coverage Δ
unittests	38.03% <ø> (+12.79%)	⬆️

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[rickyloynd-microsoft]

@sonichi fyi

@IANTHEREAL Thanks for this! Is the PR in response to an existing issue or PR? Can you provide more details on the goals of the PR?

[IANTHEREAL]

@rickyloynd-microsoft
It comes from the discussion of the PR #857, and I have updated the PR description.

[sonichi]

Small suggestions to diversify the python versions and reduce redundant work.

[IANTHEREAL]

@sonichi PTAL again