API enhancements for vector datatype

[apoorvdeshmukh]

Description

• Removed Size property since it can be inferred from SqlParameter.Value. Same as for output parameters.
  In case specified, it will be ignored.
• Changed ctor1(length) to CreateNull(length) to make it clearer that this method creats object representing null instance of given length.
• Changed SqlVector from sealed class to readonly struct.
• Test modifications to accommodate above changes.

Issues

Incorporating suggestions from #3382

Testing

Modified existing testcases for above changes.

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[Copilot]

Pull Request Overview

This PR enhances the vector datatype API by replacing the length‐based constructor with a clearer factory, removing the public Size property (now inferred), converting SqlVector<T> to a readonly struct, and updating the SQL parameter handling and tests to match.

• Refactored SqlVector<T>: made it a readonly struct, dropped the public Size property, and added CreateNull(int length).
• Updated SqlParameter to ignore Size for vector types and adjusted Prepare logic.
• Revised unit and manual tests to use CreateNull, removed direct Size assertions, and updated documentation and ref surfaces.

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlTypes/SqlVector.cs	Converted SqlVector<T> to struct, added CreateNull, removed Size property
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlParameter.cs	Skip applying Size for vector parameters and update Prepare check
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlDataReader.cs	Simplified vector‐to‐string conversion logic
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlBuffer.cs	Use CreateNull when returning a null vector
src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlTypes/SqlVectorTest.cs	Updated tests to use CreateNull and check Size via ISqlVector
src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/VectorTest/NativeVectorFloat32Tests.cs	Removed sizeInbytes, adapted test data and validation
src/Microsoft.Data.SqlClient/net*/ref/Microsoft.Data.SqlClient.cs	Updated API surface: SqlVector<T> now readonly struct, added CreateNull
doc/snippets/Microsoft.Data.SqlClient/SqlCommand.xml	Clarified in docs that Size is ignored for vectors

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (8eb9f32) to head (8ec2ca7).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #3468       +/-   ##
==========================================
- Coverage   68.86%       0   -68.87%     
==========================================
  Files         280       0      -280     
  Lines       62417       0    -62417     
==========================================
- Hits        42982       0    -42982     
+ Misses      19435       0    -19435     

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[paulmedynski]

A few minor comments.