refactor: rename packages and files to use 'flash' prefix for consistency

flash-extensions/flash-ext-view-thymeleaf/docs/fragments.md

@@ -3,11 +3,13 @@
 Use `@Fragment` for Thymeleaf fragment responses.
 
 ```java
+import models.dev.relism.flash.Request;
+
 @GET("/users/table")
 @Fragment(template = "fragments/users", value = "rows")
 public final class UsersRows extends ThymeleafHandler {
     @Override
-    public ViewModel render(dev.relism.models.Request req) {
+    public ViewModel render(Request req) {
         return ViewModel.of("users", List.of());
     }
 }