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 (e28f086) to head (513a2ef).
⚠️ Report is 122 commits behind head on develop.

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             @@
##           develop     #364      +/-   ##
===========================================
+ Coverage    86.79%   87.17%   +0.37%     
===========================================
  Files           82       82              
  Lines         3560     3665     +105     
  Branches       553      557       +4     
===========================================
+ Hits          3090     3195     +105     
+ Misses         331      330       -1     
- Partials       139      140       +1     

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[coveralls]

Coverage Report for CI Build 39342681652

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage decreased (-0.2%) to 92.737%

Details

• Coverage decreased (-0.2%) from the base build.
• Patch coverage: 4 uncovered changes across 1 file (160 of 164 lines covered, 97.56%).
• 18 coverage regressions across 6 files.

Uncovered Changes

File	Changed	Covered	%
DuckDB.NET.Data/DuckDBSchema.cs	164	160	97.56%

Coverage Regressions

18 previously-covered lines in 6 files lost coverage.

File	Lines Losing Coverage	Coverage
DuckDB.NET.Data/DataChunk/Writer/VectorDataWriterBase.cs	7	75.12%
DuckDB.NET.Data/Arrow/DuckDBArrowArrayStream.cs	3	88.46%
DuckDB.NET.Data/DuckDBAppender.cs	2	97.55%
DuckDB.NET.Data/DuckDBAppenderRow.cs	2	95.96%
DuckDB.NET.Data/DuckDBConnection.ScalarFunction.Extensions.cs	2	95.49%
DuckDB.NET.Data/DuckDBConnection.TableFunction.Extensions.cs	2	91.22%

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Coverage Stats

Relevant Lines:	4171
Covered Lines:	3932
Line Coverage:	94.27%
Relevant Branches:	2452
Covered Branches:	2210
Branch Coverage:	90.13%
Branches in Coverage %:	Yes
Coverage Strength:	965880.58 hits per line

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💛 - Coveralls

[Giorgi]

Is it ready for review?