fix(model): generate string types for decimal and money columns

[taobig]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Tests pass?	✔️
Fixed issues	#549

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.60%. Comparing base (ca976b0) to head (ccd08e1).

Files with missing lines	Patch %	Lines
src/generators/model/Generator.php	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #563      +/-   ##
============================================
+ Coverage     46.48%   46.60%   +0.12%     
  Complexity      586      586              
============================================
  Files            45       45              
  Lines          2519     2521       +2     
============================================
+ Hits           1171     1175       +4     
+ Misses         1348     1346       -2     

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[taobig]

@samdark This CI failure(Static analysis) was not introduced by this change; please review my changes.