Add tests for Runit::Config#render

What does this merge request do and why?

This merge request adds comprehensive test coverage for the Runit::Config#render method, which is a critical component of GDK's service management system responsible for setting up runit service configuration.

This MR implements tests covering:

• Directory creation (services_dir and log_dir) for both new and existing directories.
• Service processing pipeline execution in the correct order with proper arguments
• Cleanup of stale service's symlinks
• When render is called with empty services array
• Individual helper method called by render method with correct template creation and call to write the content to file
• Methods related to writing content to file with correct permission and skipping file writes in case not needed

Issue: #2897

How to set up and validate locally

1. Check out this merge request's branch.
2. Run the new tests:
   bundle exec rspec spec/lib/runit/config_spec.rb

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This MR references an issue describing the change.
• This change is backward compatible. If not, include steps to communicate to users.
• Tests added for new functionality. If not, raise an issue to follow-up.
• Observability added/updated (logging, metrics, tracing).
• Documentation added/updated.
• Announcement added for notable changes.
• gdk doctor test added.