Implement incremental syncback mode to preserve existing file structure

- Added an `incremental` flag to the `SyncbackCommand` to allow for preserving existing file structure and middleware formats during syncback operations.
- Enhanced the `syncback_loop` function to differentiate between clean mode and incremental mode, ensuring orphaned files are removed only in clean mode.
- Updated logging to reflect the mode of operation during syncback.
- Introduced new tests to validate the behavior of clean mode versus incremental mode, ensuring proper handling of orphaned files and preservation of existing structures.

rojo-test/syncback-tests/clean_mode_orphan_removal/input-project/default.project.json5

@@ -0,0 +1,10 @@
+{
+  "name": "clean_mode_orphan_removal",
+  "tree": {
+    "$className": "DataModel",
+    "ReplicatedStorage": {
+      "$className": "ReplicatedStorage",
+      "$path": "src"
+    }
+  }
+}

rojo-test/syncback-tests/clean_mode_orphan_removal/input-project/src/KeptScript.luau

@@ -0,0 +1,3 @@
+-- This script should be KEPT because the input model
+-- has a ModuleScript with the same name "KeptScript"
+print("I should be kept")

rojo-test/syncback-tests/clean_mode_orphan_removal/input-project/src/OrphanedFolder/NestedOrphan.luau

@@ -0,0 +1,3 @@
+-- This nested script should also be REMOVED
+-- when its parent folder is removed
+print("I am also orphaned")

rojo-test/syncback-tests/clean_mode_orphan_removal/input-project/src/OrphanedScript.luau

@@ -0,0 +1,3 @@
+-- This script should be REMOVED in clean mode
+-- because the input model doesn't have this script
+print("I am orphaned")