Simplify build tool selection for bun / yarn

Simplifying ahead of introducing NPM as a build tool.

Author: ksylvest

lib/tasks/cssbundling/build.rake

@@ -22,15 +22,28 @@ module Cssbundling
     extend self
 
     def install_command
-      return "bun install" if File.exist?('bun.lockb') || (tool_exists?('bun') && !File.exist?('yarn.lock'))
-      return "yarn install" if File.exist?('yarn.lock') || tool_exists?('yarn')
-      raise "cssbundling-rails: No suitable tool found for installing JavaScript dependencies"
+      case tool
+      when :bun then "bun install"
+      when :yarn then "yarn install"
+      else raise "cssbundling-rails: No suitable tool found for installing JavaScript dependencies"
+      end
     end
 
     def build_command
-      return "bun run build:css" if File.exist?('bun.lockb') || (tool_exists?('bun') && !File.exist?('yarn.lock'))
-      return "yarn build:css" if File.exist?('yarn.lock') || tool_exists?('yarn')
-      raise "cssbundling-rails: No suitable tool found for building CSS"
+      case tool
+      when :bun then "bun run build:css"
+      when :yarn then "yarn build:css"
+      else raise "cssbundling-rails: No suitable tool found for building CSS"
+      end
+    end
+
+    def tool
+      case
+      when File.exist?('bun.lockb') then :bun
+      when File.exist?('yarn.lock') then :yarn
+      when tool_exists?('bun') then :bun
+      when tool_exists?('yarn') then :yarn
+      end
     end
 
     def tool_exists?(tool)