properly shutdown litserve workers

[aniketmaurya]

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• Did you write any new necessary tests?

What does this PR do?

Fixes # (issue).

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79%. Comparing base (4823630) to head (63dc17d).

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #192   +/-   ##
===================================
  Coverage    79%    79%           
===================================
  Files        13     13           
  Lines      1030   1040   +10     
===================================
+ Hits        811    824   +13     
+ Misses      219    216    -3     

[awaelchli]

A test with a side-effect that raises an exception and asserts terminate is called would be useful here

[aniketmaurya]

thanks for the feedback @awaelchli! added a test to assert shutdown is called.