feat: update RequiredValidator to support validate empty Map, List, S…

[simonpham]

[joanpablo]

/gemini review

[joanpablo]

Hi @simonpham Thank you for the PR, really appreciate it. If possible would you mind to address the suggestions whenever you have the time?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 95.40%. Comparing base (31e3018) to head (54cc8c5). Report is 36 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/src/validators/required_validator.dart	33.33%	4 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #460      +/-   ##
==========================================
+ Coverage   95.02%   95.40%   +0.38%     
==========================================
  Files          67       66       -1     
  Lines        1386     1394       +8     
==========================================
+ Hits         1317     1330      +13     
+ Misses         69       64       -5     

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[joanpablo]

Hi @simonpham It seems like there are still some issues to solve in the PR after the change. Plase take a look whenever you have the time, and let me know if you have any questions. Thanks in advance.