Add unit test for DecodeStream and EncodeStream

[akexorcist]

Description

Add unit test to

• DecodeStream.kt
• EncodeStream.kt

Type of change

Check all that apply

• [ ] Bug fix (a non-breaking change which fixes an issue)
• [ ] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Refactoring (a change which changes the current internal or external interface)
• [ ] This change requires a documentation update
• [x] Add more unit test. No functionality changes

Checklist:

• [x] I have performed a self-review of my own code
• [x] My changes generate no new compiler warnings
• [x] New and existing unit tests pass locally with my changes

[codecov[bot]]

Codecov Report

Merging #807 (d633ef6) into master (da920c5) will increase coverage by 0.19%. The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #807      +/-   ##
============================================
+ Coverage     71.75%   71.95%   +0.19%     
  Complexity      302      302              
============================================
  Files            61       61              
  Lines          1519     1519              
  Branches        216      216              
============================================
+ Hits           1090     1093       +3     
+ Misses          316      313       -3     
  Partials        113      113              

Impacted Files	Coverage Δ	Complexity Δ
...lin/com/github/kittinunf/fuel/util/DecodeStream.kt	44.44% <0.00%> (+11.11%)	0.00% <0.00%> (ø%)
...lin/com/github/kittinunf/fuel/util/EncodeStream.kt	42.85% <0.00%> (+28.57%)	0.00% <0.00%> (ø%)

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[kittinunf]

Is this PR ready to review ^^? ❤️

[akexorcist]

Please keep this PR for a while