Refactor: Replace Object with StreamStorage for streams

The `Object` trait is too generic and has been causing confusion. This
commit introduces `StreamStorage` as a dedicated trait for reactive
stream types.

This change involves:

- Renaming `Object` to `StreamStorage` in relevant places.
- Updating the `Value::Object` enum variant to `Value::Stream`.
- Modifying how streams are handled in the compiler, VM, and tests to
  use the new `StreamStorage` trait.
- Adjusting example scripts and tests to reflect the change in type
  representation.
- The `StreamNode` struct now explicitly holds its `element_type`.

examples/record_specialization_test.myc

@@ -19,5 +19,5 @@
     )
   )
 
-  (assert-eq :StreamNode (type-of indicator))
+  (assert-eq :stream (type-of indicator))
 )