flamegraph widget: implement scroll

[laixintao]

No description provided.

[codecov-commenter]

Codecov Report

Merging #32 (e52a969) into main (10109ff) will decrease coverage by 0.51%.
The diff coverage is 40.74%.

@@            Coverage Diff             @@
##             main      #32      +/-   ##
==========================================
- Coverage   69.93%   69.43%   -0.51%     
==========================================
  Files          13       13              
  Lines         775      795      +20     
==========================================
+ Hits          542      552      +10     
- Misses        233      243      +10     

Files	Coverage Δ
flameshow/models.py	97.80% <100.00%> (+0.10%)	⬆️
flameshow/render/app.py	47.85% <0.00%> (-1.78%)	⬇️
flameshow/render/flamegraph.py	44.07% <43.75%> (+0.57%)	⬆️

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