Enhancement: Implement StringProvider

[localheinz]

This PR

• implements DataProvider\StringProvider

Follows #326.

[codecov]

Codecov Report

Merging #328 into main will decrease coverage by 21.88%.
The diff coverage is 0.00%.

@@              Coverage Diff              @@
##               main     #328       +/-   ##
=============================================
- Coverage     90.86%   68.97%   -21.89%     
- Complexity       57       65        +8     
=============================================
  Files             7        8        +1     
  Lines           186      245       +59     
=============================================
  Hits            169      169               
- Misses           17       76       +59     

Impacted Files	Coverage Δ	Complexity Δ
src/DataProvider/StringProvider.php	0.00% <0.00%> (ø)	8.00 <8.00> (?)

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