Add duplicate name check for subclasses

[shunichironomura]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 79.75%. Comparing base (bb8006f) to head (c194e22).

Files	Patch %	Lines
capsula/_context/_base.py	33.33%	2 Missing ⚠️
capsula/_reporter/_base.py	33.33%	2 Missing ⚠️
capsula/_watcher/_base.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #207      +/-   ##
==========================================
- Coverage   80.00%   79.75%   -0.25%     
==========================================
  Files          29       29              
  Lines         890      899       +9     
==========================================
+ Hits          712      717       +5     
- Misses        178      182       +4     

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