Migrate to ESM and upgrade dependencies (#752)

* Migrate to ESM and upgrade dependencies

* Address review: use type-only import for QualityOptions

* update version to 6.0.0 in package.json and package-lock.json

* Add ESM migration note to README for V6

* Update test imports for ESM and clean up devDependencies (ts-node, @types/jest)

* Pin @types/node to 24.x and refine tsconfig/README wording

dist/cache-save/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}

dist/setup/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}