Refactored entity serialization

[AndreasLrx]

Description

Rework of entity serialization with explicit type registration using a macro.

Close #150 (again)

What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Optimization
• Documentation Update

[optional] Minor fixes

Fix Registry.getSystem: It was looking in the storages instances instead of the system instances

Added/updated tests?

• New tests written
• Existing tests updated
• Tests are not required because this is a documentation update
• I need help with writing tests

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.59%. Comparing base (cfc7649) to head (3f96a79).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
+ Coverage   82.23%   82.59%   +0.36%     
==========================================
  Files          64       64              
  Lines        1103     1103              
  Branches      353      353              
==========================================
+ Hits          907      911       +4     
+ Misses        140      135       -5     
- Partials       56       57       +1     

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