feat: use asyncio

[DeadNews]

• feat: use asyncio
• feat: replace requests with httpx
• feat: bump minimal python version to 3.9
• feat: replace kdialog with notify-send, make optional
• feat: remove hosting pictshare (discontinued)
• test: increase coverage

[codecov-commenter]

Codecov Report

Merging #106 (08c74bc) into main (b2ebb0e) will increase coverage by 47.21%.
The diff coverage is 94.87%.

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@@             Coverage Diff             @@
##             main     #106       +/-   ##
===========================================
+ Coverage   49.00%   96.21%   +47.21%     
===========================================
  Files           5        5               
  Lines         251      238       -13     
===========================================
+ Hits          123      229      +106     
+ Misses        128        9      -119     

Impacted Files	Coverage Δ
src/images_upload_cli/util.py	94.23% <80.00%> (+0.11%)	⬆️
src/images_upload_cli/cli.py	94.87% <95.00%> (+1.32%)	⬆️
src/images_upload_cli/upload.py	97.18% <95.60%> (+72.18%)	⬆️
src/images_upload_cli/__init__.py	100.00% <100.00%> (ø)