Implement new oneshot Vfs for CLI commands and enhance JSON5 serialization

- Added `new_oneshot` method to the Vfs struct, providing a backend suitable for one-time operations without file watching.
- Updated CLI commands (`fmt_project` and `syncback`) to utilize the new oneshot Vfs, improving error handling during file operations.
- Enhanced JSON5 serialization by introducing a custom serializer that directly builds a tree structure, improving performance and maintaining sorted keys.
- Improved error logging in JSON serialization to provide more context on failures.

tests/rojo_test/internable.rs

@@ -58,7 +58,7 @@ impl<'a> Internable<&'a HashMap<Ref, Instance<'_>>> for Instance<'a> {
 
 impl Internable<()> for SocketPacket<'_> {
     fn intern(&self, redactions: &mut RedactionMap, extra: ()) {
-        redactions.intern(&self.session_id);
+        redactions.intern(self.session_id);
         match &self.body {
             SocketPacketBody::Messages(packet) => packet.intern(redactions, extra),
         }