Extract adders updates

[aletempiac]

This PR includes:

• Adding tests for decompose_multioutput util
• Fixes in decompose_multioutput util
• Experiment for extract_adder
• Comments in block_network to help the user understanding how HAs and FAs are created

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (1134d1d) 83.68% compared to head (4fdb61d) 83.59%.

Files	Patch %	Lines
.../algorithms/experimental/decompose_multioutput.hpp	75.00%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #631 +/- ## ========================================== - Coverage 83.68% 83.59% -0.09% ========================================== Files 186 187 +1 Lines 29617 29740 +123 ========================================== + Hits 24784 24862 +78 - Misses 4833 4878 +45 ```

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