feat(bindings): auto-detect scanners

cli/src/templates/package.swift

@@ -1,6 +1,13 @@
 // swift-tools-version:5.3
+
+import Foundation
 import PackageDescription
 
+var sources = ["src/parser.c"]
+if FileManager.default.fileExists(atPath: "src/scanner.c") {
+    sources.append("src/scanner.c")
+}
+
 let package = Package(
     name: "TreeSitterCAMEL_PARSER_NAME",
     products: [
@@ -14,10 +21,7 @@ let package = Package(
             name: "TreeSitterCAMEL_PARSER_NAME",
             dependencies: [],
             path: ".",
-            sources: [
-                "src/parser.c",
-                // NOTE: if your language has an external scanner, add it here.
-            ],
+            sources: sources,
             resources: [
                 .copy("queries")
             ],