Tests | Refactor NativeVectorFloat32Tests for future Half support

[edwardneal]

Description

This is somewhat inspired by #4234. We don't yet have support for SqlVector<Half> and other types, but this should hopefully make the test logic trivial to add.

I'd recommend moving commit by commit - the introduction of a base class has resulted in the PR looking much larger than it truly is.

The overall design is now more generic. We have:

• NativeVectorTestDataBase<TElement>, which contains test data for SqlVector<TElement>
• NativeVectorTestsBase<TElement, TTestData>, which contains the test logic and links it to the test data
• VectorFloat32TestData: derived from NativeVectorTestDataBase which contains float-based sample data
• NativeVectorFloat32Tests: the same tests and the same logic as in main, but derived from NativeVectorTestsBase

Adding future support for Half should mean simply introducing VectorFloat16TestData and NativeVectorFloat16Tests classes:

public sealed class VectorFloat16TestData : NativeVectorTestDataBase<Half>
{
    public override Half[] SampleScalarData => [1, 2, 3, 4, 5, 6];

    public override Half[,] SampleDataSet => /* */;

    public override int IncorrectScalarDataParameterSize => 9999;

    public override bool IsSupported => DataTestUtility.IsSqlVectorFloat16Supported;

    public override string SqlServerTypeName => "float16";
}

public sealed class NativeVectorFloat16Tests : NativeVectorTestsBase<Half, VectorFloat16TestData>
{
}

I've also made a handful of hygiene improvements, but none are particularly controversial:

• Use of RAII primitives
• Text corrections in comments
• Assertion cleanups (catching an exception and running Assert.Fail, performing Assert.True(!verifyReader.IsDBNull(0), ...), etc.)
• Nullability annotations

Issues

In lieu of any more specific issue for Half/float16 support for SqlVector, this contributes to #3444.

Testing

All automated tests continue to pass.