fix: Allow to make annotated collection members optional

[borchero]

Motivation

This PR fixes two issues in one:

• Annotating optional collection members currently fails with the following issue:

  TypeError: issubclass() arg 1 must be a class
  

• Even if that did not fail, inlining optional collection members for sampling would fail due to a missing flag

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (54cbc75) to head (c6d4910).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #8   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           36        36           
  Lines         1788      1785    -3     
=========================================
- Hits          1788      1785    -3     

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