.NET: Updated package versions for RC release

[dmytrostruk]

Motivation and Context

• Updated nuget-package.props to support release candidate versioning with a central RCNumber property
• Packages marked with IsReleaseCandidate=true now produce 1.0.0-rc1 instead of date-based preview/alpha suffixes
• Marked 11 packages for RC promotion per .NET: Release candidate packages #3912: AI, Abstractions, Anthropic, AzureAI, Declarative, OpenAI, Purview, Workflows, Workflows.Declarative, Workflows.Declarative.AzureAI, and Workflows.Generators
• Non-RC packages continue to use their existing preview/alpha versioning unchanged

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 packaging/versioning configuration to support Release Candidate (RC) NuGet versions via a central RCNumber and a per-project IsReleaseCandidate opt-in, promoting a defined set of libraries to 1.0.0-rcN while leaving other packages on the existing preview/alpha scheme.

Changes:

• Added RCNumber and conditional RC PackageVersion logic to dotnet/nuget/nuget-package.props.
• Marked selected projects as RC via <IsReleaseCandidate>true</IsReleaseCandidate> in their .csproj files.
• Refreshed the date-based preview/alpha version stamp for non-RC packages.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
dotnet/nuget/nuget-package.props	Introduces centralized RC versioning logic and retains date-stamped preview/alpha versions for non-RC builds.
dotnet/src/Microsoft.Agents.AI/Microsoft.Agents.AI.csproj	Marks core AI package as RC.
dotnet/src/Microsoft.Agents.AI.Abstractions/Microsoft.Agents.AI.Abstractions.csproj	Marks Abstractions package as RC.
dotnet/src/Microsoft.Agents.AI.Anthropic/Microsoft.Agents.AI.Anthropic.csproj	Marks Anthropic package as RC.
dotnet/src/Microsoft.Agents.AI.AzureAI/Microsoft.Agents.AI.AzureAI.csproj	Marks AzureAI package as RC.
dotnet/src/Microsoft.Agents.AI.Declarative/Microsoft.Agents.AI.Declarative.csproj	Marks Declarative package as RC.
dotnet/src/Microsoft.Agents.AI.OpenAI/Microsoft.Agents.AI.OpenAI.csproj	Marks OpenAI package as RC.
dotnet/src/Microsoft.Agents.AI.Purview/Microsoft.Agents.AI.Purview.csproj	Marks Purview package as RC.
dotnet/src/Microsoft.Agents.AI.Workflows/Microsoft.Agents.AI.Workflows.csproj	Marks Workflows package as RC.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Microsoft.Agents.AI.Workflows.Declarative.csproj	Marks Workflows.Declarative package as RC and normalizes whitespace.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative.AzureAI/Microsoft.Agents.AI.Workflows.Declarative.AzureAI.csproj	Marks Workflows.Declarative.AzureAI package as RC.
dotnet/src/Microsoft.Agents.AI.Workflows.Generators/Microsoft.Agents.AI.Workflows.Generators.csproj	Marks Workflows.Generators package as RC.

Comments suppressed due to low confidence (1)

dotnet/src/Microsoft.Agents.AI.Declarative/Microsoft.Agents.AI.Declarative.csproj:8

• IsPackable is set to false before importing nuget-package.props, but that props file sets IsPackable to true, so this project will still be packable. If this package is intended to ship (especially now that IsReleaseCandidate is true), remove the IsPackable override; if it’s meant to stay non-packable, move the IsPackable=false setting to after the import so it actually takes effect.

    <IsReleaseCandidate>true</IsReleaseCandidate>
    <VersionSuffix>preview</VersionSuffix>
    <NoWarn>$(NoWarn);MEAI001</NoWarn>
    <IsPackable>false</IsPackable>
  </PropertyGroup>

[lokitoth]

Core Workflows packages all look good