Standardize images in encoding documentation

[MatteoRobbiati]

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.85%. Comparing base (68309e1) to head (4d29173).

Additional details and impacted files

@@                  Coverage Diff                  @@
##           entangling_layer_doc    #1278   +/-   ##
=====================================================
  Coverage                 99.85%   99.85%           
=====================================================
  Files                        73       73           
  Lines                     10638    10638           
=====================================================
  Hits                      10623    10623           
  Misses                       15       15           

Flag	Coverage Δ
unittests	99.85% <ø> (ø)

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