ci : move release workflow to a separate file

[slaren]

• Moves the workflow to generate releases to release.yml. While this adds some code duplication, it makes the workflow easier to understand and maintain.
• The releases now only include the tools, instead of all examples and tests
• Adds actions to install CUDA toolkit and determine tag names to reduce code duplication

Test run: https://github.com/slaren/llama.cpp/actions/runs/14888774492
Test release: https://github.com/slaren/llama.cpp/releases/tag/b5308

[Copilot]

Pull Request Overview

This PR extracts the release workflow into a separate file and refines the release process to include only the necessary tools. It adds a new Windows setup action for installing specific CUDA Toolkit versions and a tag name determination action to streamline release naming.

• Introduces a Windows CUDA Toolkit setup action supporting versions 11.7 and 12.4.
• Implements an action to compute the release tag name based on the branch and commit count.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
.github/actions/windows-setup-cuda/action.yml	Adds composite steps to install CUDA Toolkit for two versions on Windows using PowerShell.
.github/actions/get-tag-name/action.yml	Adds a composite action to determine the release’s tag name based on the current branch.