Remove unused symlink code

[bachand]

In working on #32 I realized that there's unused symlink Ruby code. I'm going to remove this code since it's always possible to restore it from the git history if necessary.

I ran ./bin/battlestation setup locally. I removed the symlink to my .zshrc file and verified that the symlink was created by the setup script.

[Copilot]

Pull Request Overview

This PR removes unused symlink functionality from the Battlestation project. The symlink feature appears to have been partially implemented but never completed or utilized.

• Removes the incomplete Battlestation::Symlink class and its test file
• Deletes the unused symlinks configuration file
• Updates GitHub Actions workflow to use newer action versions and bundler cache

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
spec/battlestation/symlink_spec.rb	Removes incomplete test file for symlink functionality
lib/battlestation/symlink.rb	Removes the incomplete Symlink class with unimplemented methods
lib/battlestation.rb	Removes the require statement for the deleted symlink module
config/symlinks.yaml	Removes configuration file that defined symlink mappings
.github/workflows/ruby.yml	Updates GitHub Actions to use newer checkout versions and bundler cache

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[bachand]

This tool is only meant to support macOS.

[bachand]

We were previously returning the exit status from the last time we called into the shell without considering the previous shell invocations. I think it's preferable to avoid returning an exit status until orunless we can return one that's more meaningful.