Remove inheritance from common::Singleton for all classes

[iche033]

🦟 Bug fix

Summary

Continuing the effort from #874, this PR removes inheritance from common::Singleton for all other classes.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #876 (50c9300) into main (a1d4e87) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 50c9300 differs from pull request most recent head f34ce02. Consider uploading reports for the commit f34ce02 to get more accurate results

@@           Coverage Diff           @@
##             main     #876   +/-   ##
=======================================
  Coverage   75.09%   75.09%           
=======================================
  Files         176      176           
  Lines       16859    16859           
=======================================
  Hits        12661    12661           
  Misses       4198     4198           

Files Changed	Coverage Δ
...e2/include/gz/rendering/ogre2/Ogre2RenderEngine.hh	100.00% <ø> (ø)
ogre2/src/Ogre2RenderEngine.cc	68.18% <100.00%> (ø)