Add DoNotHashLeaves config

[alrevuelta]

• [x] Add a new configuration flag DoNotHashLeaves to avoid hashing the leafs of the tree. This is specifically useful when the input to the tree (leafs) were already concatenated/hashed in a different way that differs from the HashFunc.
• [x] Add tests to the new feature.

[alrevuelta]

If you think this feature is relevant for the repo, I can add tests.

[codecov[bot]]

Codecov Report

Merging #22 (f2a5383) into main (2927e5b) will increase coverage by 0.10%. The diff coverage is 70.00%.

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   92.51%   92.62%   +0.10%     
==========================================
  Files           2        2              
  Lines         481      488       +7     
==========================================
+ Hits          445      452       +7     
  Misses         24       24              
  Partials       12       12              

Impacted Files	Coverage Δ
merkle_tree.go	92.50% <70.00%> (+0.11%)	:arrow_up:

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[txaty]

Thanks for contributing. This is a very good feature to add. Would you please add some unit tests to it?

[alrevuelta]

@txaty Done!

[txaty]

LGTM