libs: add module encoding_utils

[glarrain]

Includes these functions:

• clean_base64
• decode_base64_strict
• validate_base64

[codecov-io]

Codecov Report

Merging #27 into develop will decrease coverage by 1.46%.
The diff coverage is 26.08%.

@@             Coverage Diff             @@
##           develop      #27      +/-   ##
===========================================
- Coverage    70.12%   68.65%   -1.47%     
===========================================
  Files           14       15       +1     
  Lines          666      689      +23     
  Branches        87       89       +2     
===========================================
+ Hits           467      473       +6     
- Misses         164      181      +17     
  Partials        35       35

Impacted Files	Coverage Δ
cl_sii/libs/encoding_utils.py	26.08% <26.08%> (ø)

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