Add commas, decimals to weekly-new-cases field and prevent non-numeric inputs. Remove default 0 value when empty or at beginning of string

[CloudByteKS]

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[codecov]

Codecov Report

Merging #1848 (24aafcd) into main (360b70c) will decrease coverage by 0.10%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##             main    #1848      +/-   ##
==========================================
- Coverage   66.00%   65.91%   -0.10%     
==========================================
  Files         104      104              
  Lines        2833     2843      +10     
  Branches      513      512       -1     
==========================================
+ Hits         1870     1874       +4     
- Misses        813      818       +5     
- Partials      150      151       +1     

Files Changed	Coverage Δ
.../calculator/prevalence/ManualPrevalenceDetails.tsx	51.21% <46.15%> (-3.62%)	⬇️

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