Upgrade to SLNX

[ryanlua]

Upgrades the project to use SLNX instead of SLN

[Copilot]

Pull Request Overview

This PR upgrades the project to use the newer SLNX format instead of the traditional SLN format for Visual Studio solutions. This migration provides benefits like simplified XML-based configuration and better version control integration.

• Adds a new FluentAutoClicker.slnx file with XML-based solution configuration
• Updates the CI workflow to reference the new SLNX file
• Removes the legacy FluentAutoClicker.sln file

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
FluentAutoClicker.slnx	New XML-based solution file defining project and platform configurations
FluentAutoClicker.sln	Legacy solution file removed as part of migration
.github/workflows/ci.yml	CI workflow updated to build with the new SLNX file

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