pyvm: split op handlers into ops_core/ops_box/ops_ctrl; add ops_flow + intrinsic; delegate vm.py without behavior change

net-plugin: modularize constants (consts.rs) and sockets (sockets.rs); remove legacy commented socket code; fix unused imports
mir: move instruction unit tests to tests/mir_instruction_unit.rs (file lean-up); no semantic changes
runner/pyvm: ensure using pre-strip; misc docs updates

Build: cargo build ok; legacy cfg warnings remain as before

apps/tests/macro/loopform/nested_if_continue.nyash

@@ -0,0 +1,14 @@
+local i = 0
+loop(i < 6) {
+  if (i % 2 == 0) {
+    if (i == 4) {
+      i = i + 1
+      continue
+    }
+    i = i + 1
+    continue
+  }
+  print(i)
+  i = i + 1
+}
+