Update UnbrandedGeneratorVersion to 1.0.0-alpha.20260122.1

[Copilot]

Description

Updates the UnbrandedGeneratorVersion property and TypeSpec HTTP Client C# dependency to version 1.0.0-alpha.20260122.1.

• TypeSpec commit: microsoft/typespec@a1b401b

Changes Made

• Updated eng/Packages.Data.props UnbrandedGeneratorVersion property
• Updated eng/packages/http-client-csharp/package.json dependency version
• Ran npm install to update package-lock.json
• Ran eng/packages/http-client-csharp/eng/scripts/Generate.ps1 to regenerate test projects
• Generated emitter-package.json artifacts using tsp-client
• Verified test library generation is current (no additional changes on regeneration)

This is an automated PR created by the TypeSpec publish pipeline.

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This checklist is used to make sure that common guidelines for a pull request are followed.

• Please add REST spec PR link to the SDK PR
• I have read the contribution guidelines.
• The pull request does not introduce breaking changes.

General Guidelines

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

SDK Generation Guidelines

• If an SDK is being regenerated based on a new swagger spec, a link to the pull request containing these swagger spec changes has been included above.
• The generate.cmd file for the SDK has been updated with the version of AutoRest, as well as the commitid of your swagger spec or link to the swagger spec, used to generate the code.
• The *.csproj and AssemblyInfo.cs files have been updated with the new version of the SDK.

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