feat: clean up use date picker

[flaminic]

Refactoring useDatePicker:

• Remove isValid, errorMessage, and warningMessage as we are using validateDateString directly.
• Remove calendarDate as well, since we don't want to expose it anymore

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.32%. Comparing base (6770573) to head (371a08f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/utils/helpers.ts	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
+ Coverage   91.25%   91.32%   +0.06%     
==========================================
  Files          56       56              
  Lines        1201     1199       -2     
  Branches      326      328       +2     
==========================================
- Hits         1096     1095       -1     
+ Misses        103      102       -1     
  Partials        2        2              

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