Add ENUM column

[vjik]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	✔️

Related to yiisoft/db#1107

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.64%. Comparing base (0f41835) to head (724c325).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #415      +/-   ##
============================================
+ Coverage     98.62%   98.64%   +0.02%     
- Complexity      247      251       +4     
============================================
  Files            26       26              
  Lines           800      812      +12     
============================================
+ Hits            789      801      +12     
  Misses           11       11              

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[Copilot]

Pull request overview

This PR adds support for ENUM column types in the MSSQL database driver. Since MSSQL doesn't have a native ENUM type, this implementation uses NVARCHAR columns with CHECK constraints to simulate enum behavior.

Key Changes:

• Enum value extraction from CHECK constraints via regex pattern matching
• ENUM type mapping to NVARCHAR with appropriate CHECK constraint generation
• Comprehensive test coverage including edge cases for non-enum CHECK constraints

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/Schema.php	Adds tryGetEnumValuesFromCheck() method to extract enum values from MSSQL CHECK constraint definitions and integrates it into column loading
src/Column/ColumnDefinitionBuilder.php	Adds ENUM type mapping to nvarchar and refactors buildCheck() to delegate to parent class for ENUM handling
tests/Column/EnumColumnTest.php	Adds MSSQL-specific enum column tests, including negative test cases for non-enum CHECK constraints
CHANGELOG.md	Documents the new enumeration column type support feature

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