Add Windows Build Workflow (GitHub Actions)

[Thireus]

First, thank you for maintaining this project — it has been very useful, and I appreciate the work that has gone into it.

I initially created a fork to add automated Windows builds for my own use, since I needed ready-to-use binaries. Since this is functionality that could benefit other users as well, I’m submitting this pull request so the Windows build workflow can live directly in the main repository instead of in my fork.

This PR includes:

1. GitHub Actions workflow for building the project on Windows
   

2. Automatic artifact uploads so users can download ready-to-use Windows builds
   

3. Other small tweaks to ensure the code compiles on Windows.
   

Builds must be manually triggered (I believe they could be automated after each commit, but I have not had the chance to dig into it). There is also a bit of cleanup to do, specifically regarding other automated jobs that run to conduct meaningless checks. The original code was obtained from mainline with some tweaking to adapt it to ik_llama.cpp.

My goal was to make the project more accessible to Windows users, specifically users who do not find the time to set up a dev env or don't have the knowledge to do it on Windows, such as myself. If you’d prefer changes to structure, naming, workflow triggers, or anything else, I’m happy to adjust the PR accordingly.

Thanks again for the project and for taking the time to review this!