feat(isNumeric): add support for thousand separator option

[PepiPetrov]

This fixes #1433 and resolves merge conflicts of #1476 .

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7fdc788) to head (c0152d1).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2711   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2587      2611   +24     
  Branches       656       660    +4     
=========================================
+ Hits          2587      2611   +24     

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[tux-tn]

Thank you for your contribution and for taking the time to work on the old PR. I added some code recommendations in my review but I have also a general concern about the thousands_separator value. As discussed in the original PR (#1476), , I agree on limiting its value to a list of standard separators like comma, dot, space and underscore.