Fix the bad filename bug

[habedi]

• Fixed this bug: Downloaded files are missing their extension #84 and added a few tests to prevent regression.
• Added a few missing uni tests.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 25.59%. Comparing base (4e65b2e) to head (c5afb3e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
client/download.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #85      +/-   ##
==========================================
+ Coverage   25.20%   25.59%   +0.39%     
==========================================
  Files          40       40              
  Lines        4107     4106       -1     
==========================================
+ Hits         1035     1051      +16     
+ Misses       2945     2916      -29     
- Partials      127      139      +12     

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