.NET: Updating dotnet package versions for 1.9 release

[alliscode]

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Updates the centralized .NET NuGet packaging version metadata to align the repository’s package versioning with the upcoming 1.9 release.

Changes:

• Bumped the central <VersionPrefix> from 1.8.0 to 1.9.0.
• Updated <DateSuffix> to 260603 to reflect the current build date stamp.
• Updated <GitTag> from 1.8.0 to 1.9.0.

Show a summary per file

File	Description
dotnet/nuget/nuget-package.props	Updates centralized NuGet package version/tag values used by .NET projects importing this props file.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0

[github-actions]

Automated Code Review

Reviewers: 4 | Confidence: 84% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Design Approach

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