Format vector floats with the invariant culture in SqlServerVectorTyp…

[ilkertskn]

…eMapping

• GenerateNonNullSqlLiteral appended each float via StringBuilder.Append(float), which formats with the current culture, so a vector literal such as CAST('[1.5,2.5]' AS VECTOR(2)) became CAST('[1,5,2,5]' AS VECTOR(2)) under cultures with a comma decimal separator (e.g. de-DE)
• Format each float with "R" and CultureInfo.InvariantCulture, matching FloatTypeMapping
• Add a test under a non-invariant culture

• I've read the guidelines for contributing and seen the walkthrough
• I've posted a comment on an issue with a detailed description of how I am planning to contribute and got approval from a member of the team
• The code builds and tests pass locally (also verified by our automated build checks)
• Commit messages follow this format:

        Summary of the changes
        - Detail 1
        - Detail 2

        Fixes #bugnumber

• Tests for the changes have been added (for bug fixes / features)
• Code follows the same patterns and style as existing code in this repo

[ilkertskn]

@dotnet-policy-service agree

[Copilot]

Pull request overview

Fixes SQL Server vector SQL literal generation to be culture-invariant when formatting float elements, preventing incorrect decimal separators under non-invariant cultures.

Changes:

• Format vector float elements with "R" and CultureInfo.InvariantCulture in SqlServerVectorTypeMapping.GenerateNonNullSqlLiteral.
• Add a regression test running under de-DE to validate invariant-culture formatting for vector literals.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/EFCore.SqlServer/Storage/Internal/SqlServerVectorTypeMapping.cs	Formats float vector elements using invariant culture to avoid culture-dependent decimal separators in generated SQL literals.
test/EFCore.SqlServer.Tests/Storage/SqlServerTypeMappingTest.cs	Adds a de-DE culture regression test ensuring generated vector SQL literals use . as decimal separator.