perf: write to disk only when progress updated

[monkeyWie]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 39.13043% with 14 lines in your changes missing coverage. Please review.

Project coverage is 58.82%. Comparing base (f4876c8) to head (c55f8d6).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/download/downloader.go	39.13%	10 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #839      +/-   ##
==========================================
+ Coverage   58.80%   58.82%   +0.02%     
==========================================
  Files          35       35              
  Lines        4464     4474      +10     
==========================================
+ Hits         2625     2632       +7     
  Misses       1567     1567              
- Partials      272      275       +3     

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