Fix array Contains under C# 14

[phnx47]

C# 14 binds array.Contains to MemoryExtensions.Contains, wrapping the collection in an implicit span conversion. The IN values resolved to null, silently degrading the predicate to IS NOT NULL. Unwrap the conversion and pin LangVersion to 14.0.

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.03%. Comparing base (d18ad3a) to head (3b8d0c3).

Files with missing lines	Patch %	Lines
src/SqlGenerator/ExpressionHelper.cs	62.50%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #578      +/-   ##
==========================================
- Coverage   64.08%   64.03%   -0.05%     
==========================================
  Files          59       59              
  Lines        1985     1991       +6     
  Branches      392      394       +2     
==========================================
+ Hits         1272     1275       +3     
- Misses        572      573       +1     
- Partials      141      143       +2     

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