Simplify tuple flattening and destructuring

The `flatten_tuple` function was unnecessarily recursive. It can now
simply return the elements of the tuple directly. The VM's destructuring
logic has been updated to handle nested destructuring more efficiently.
A new integration test case for multi-level destructuring has been
added.

examples/tuple-struct.myc

@@ -0,0 +1,12 @@
+(do
+     (def pipe (fn [conf]
+       (do
+          (def [str s] conf)
+          (def [f ss] s)
+          ["Symbol:" str "field:" f "id:" ss]
+       )
+      )
+     )
+
+     (pipe ["btc" [:close "cls"]])
+   )