Add enum PHPType::class and refactor getColumnPhpType() method in Schema::class.

[terabytesoftw]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌
Fixed issues	#57

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.

Project coverage is 66.51%. Comparing base (d43c1d1) to head (6ce3172).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/db/mysql/Schema.php	85.71%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #91      +/-   ##
============================================
- Coverage     66.52%   66.51%   -0.01%     
- Complexity    11217    11221       +4     
============================================
  Files           433      433              
  Lines         36456    36459       +3     
============================================
+ Hits          24251    24252       +1     
- Misses        12205    12207       +2     

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