Improve source file detection and tests

- Use SwiftPM-provided sourceFiles for filtering - Add Utils.swift with
URL descendant check - Update example to use Views/ instead of Folder/ -
Add test for non-included Swift file - Update .zed settings to disable
VSCode CSS language server

Tests/SwiftTailwindTests/Tests.swift

@@ -21,6 +21,10 @@ struct SwiftTailwindExampleTests {
       generatedCSS?.contains("bg-red-100") == true,
       "Arbitary value class used in Folder/Template.swift is generated."
     )
+    #expect(
+      generatedCSS?.contains("text-sm") == false,
+      "Class used in other non-included Swift code is not generated."
+    )
     #expect(
       generatedCSS?.contains("bg-blue-500") == false,
       "Class not used is not generated."