polish(yzj): polish render and add practice demo

[jayyoung0802]

No description provided.

[codecov]

Codecov Report

Merging #56 (1de39c2) into main (71eb660) will increase coverage by 0.59%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
+ Coverage   85.24%   85.83%   +0.59%     
==========================================
  Files          87       87              
  Lines        4499     4505       +6     
==========================================
+ Hits         3835     3867      +32     
+ Misses        664      638      -26     

Flag	Coverage Δ
unittests	85.83% <14.28%> (+0.59%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
gobigger/render/realtime_render.py	63.77% <14.28%> (-3.17%)	⬇️

... and 5 files with indirect coverage changes