Improve compression of enhanced

[Radonirinaunimi]

This PR implement the following changes:

• Pre-process the enhanced set by removing duplicates (if there are).
• Shuffle the resulting pre-processed set prior to compression while keeping track of the indices. Previously, prior and synthetics are just layered on top of each other which presumably increases the likelihood that the minimizer is trapped in some local minima.

[codecov]

Codecov Report

Merging #40 (8d9b0ba) into master (760a665) will not change coverage.
The diff coverage is 0.00%.

@@          Coverage Diff           @@
##           master     #40   +/-   ##
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  Coverage    0.00%   0.00%           
======================================
  Files          15      15           
  Lines        1335    1359   +24     
======================================
- Misses       1335    1359   +24     

Flag	Coverage Δ
unittests	0.00% <0.00%> (ø)

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Impacted Files	Coverage Δ
src/pycompressor/compressing.py	0.00% <0.00%> (ø)
src/pycompressor/compressor.py	0.00% <0.00%> (ø)
src/pycompressor/errfunction.py	0.00% <0.00%> (ø)
src/pycompressor/utils.py	0.00% <0.00%> (ø)

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