Support ADO.NET schema data types and metadata probing

[alaricd]

Summary

• Add standard DataSourceInformation metadata needed by ADO.NET schema probing.
• Add DataTypes metadata for DuckDB native types.
• Align metadata column ordering, types, normalized versions, DBNull values, and restriction validation with the common ADO.NET contract.
• Correct index restriction metadata.
• Add focused schema coverage.

Validation

• dotnet test DuckDB.NET.Test/Test.csproj --no-restore --filter FullyQualifiedName~SchemaTests -m:1
• 23 tests passed.

[codecov]

Codecov Report

❌ Patch coverage is 99.09091% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.17%. Comparing base (79857ba) to head (513a2ef).
⚠️ Report is 222 commits behind head on main.

Files with missing lines	Patch %	Lines
DuckDB.NET.Data/DuckDBSchema.cs	99.09%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #364      +/-   ##
==========================================
- Coverage   88.09%   87.17%   -0.92%     
==========================================
  Files          65       82      +17     
  Lines        2310     3665    +1355     
  Branches      322      557     +235     
==========================================
+ Hits         2035     3195    +1160     
- Misses        202      330     +128     
- Partials       73      140      +67     

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[coveralls]

Coverage Report for CI Build 38652328885

Warning

No base build found for commit 05ef6f0 on main.
Coverage changes can't be calculated without a base build.
If a base build is processing, this comment will update automatically when it completes.

Coverage: 88.732%

Details

• Patch coverage: 110 of 110 lines across 1 file are fully covered (100%).

Uncovered Changes

No uncovered changes found.

Coverage Regressions

Requires a base build to compare against. How to fix this →

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Coverage Stats

Relevant Lines:	3665
Covered Lines:	3335
Line Coverage:	91.0%
Relevant Branches:	1935
Covered Branches:	1634
Branch Coverage:	84.44%
Branches in Coverage %:	Yes
Coverage Strength:	407270.02 hits per line

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💛 - Coveralls

[Giorgi]

Is it ready for review?