.NET: Update version for release

[westey (westey-m)]

Motivation and Context

Description

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 .NET NuGet packaging metadata to prepare the next release by bumping the central package version identifiers.

Changes:

• Bump NuGet VersionPrefix from 1.3.0 to 1.4.0.
• Update DateSuffix to 260505 and GitTag to 1.4.0 to match the new release version.

[github-actions]

Automated Code Review

Reviewers: 4 | Confidence: 82% | Result: All clear

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

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Automated review by westey-m's agents