refactor: come back top a monolithic file structure

[12rambau]

That was the original design of the lib. Due to filename conflic with previous implementaion (where the only diffrence was the capital letter) we decided to move all the extention Accesors to dedicated sub-packages. Now that we cleaned the repository from nearly all the deprecated files, there is real-estate available to move back the Accessors at the root of the package.

1. The first nice effect is readability, as every accessor is living in a self contained module instead of the init.py of each subpackage, you will no longer have 7 tabs with the saame name in your code editor
2. relative import: as the files are now at the top of the foodchain we can rely again on relative import with going up he hierarchy ladder
3. nice side effect in the documentation as the API interpretation is loosing a intermediate (and useless) layer for each accessor.

It should not change anythng from a user persepective so changes were done in the tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.75%. Comparing base (0497ded) to head (b2dac78).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #321   +/-   ##
=======================================
  Coverage   90.75%   90.75%           
=======================================
  Files          27       27           
  Lines        1352     1352           
  Branches      145      145           
=======================================
  Hits         1227     1227           
  Misses        105      105           
  Partials       20       20           

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