Reduce time complexity for chain of * in problem filter

[quantum5]

This has not been integration tested, but the snippets work.

[codecov-commenter]

Codecov Report

Merging #1658 (d7ab327) into master (c0dbc8c) will increase coverage by 0.00%.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##           master    #1658   +/-   ##
=======================================
  Coverage   46.24%   46.25%           
=======================================
  Files         215      215           
  Lines       12279    12282    +3     
=======================================
+ Hits         5679     5681    +2     
- Misses       6600     6601    +1     

Impacted Files	Coverage Δ
judge/tasks/user.py	24.63% <50.00%> (+1.91%)	⬆️

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[Ninjaclasher]

Hmm it seems I didn't run into this because this exact issue was fixed in Python 3.9 (commit) and I was on Python 3.9 instead of Python 3.8. It might be good to add a comment saying this was fixed in Python 3.9, but we need the regex to be sure nothing bad happens for < 3.9.