Gazebo launcher engine refactored

[pariaspe]

Basic Info

Info	Please fill out this column
Issue(s) this addresses	-
ROS2 version tested on	Humble
Aerial platform tested on	Ignition

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Description of contribution in a few bullet points

• JSON world description are now validated through pydantic
• Data models are simplified and reorganized, parsing is no longer done manually

[codecov-commenter]

Codecov Report

Merging #232 (58ed464) into main (8b6fa67) will increase coverage by 0.07%.
The diff coverage is n/a.

❗ Current head 58ed464 differs from pull request most recent head f85b839. Consider uploading reports for the commit f85b839 to get more accurate results

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@@           Coverage Diff            @@
##            main    #232      +/-   ##
========================================
+ Coverage   3.07%   3.14%   +0.07%     
========================================
  Files        100     100              
  Lines       5244    5311      +67     
  Branches     451     476      +25     
========================================
+ Hits         161     167       +6     
- Misses      4945    4978      +33     
- Partials     138     166      +28     

Flag	Coverage Δ
unittests	3.14% <ø> (+0.07%)	⬆️

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see 22 files with indirect coverage changes

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