Add changset for v3

.changeset/polite-books-serve.md

@@ -0,0 +1,13 @@
+---
+'bun-stimulus-plugin': major
+---
+
+## BREAKING CHANGES
+
+Remove the `directorySeparator` option and replace all `_` by `-` to follow the Stimulus naming convention.
+
+If you previously had a controller named `my_controller`, it will now be `my-controller`.
+
+## Dev Changes
+
+Update ESLint to flat config, update dependencies.