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/exception/expr_postfix_direct.nyash

@@ -0,0 +1,12 @@
+function f(x) {
+  return x
+}
+
+function main(args) {
+  local i = 0
+  loop(i < 2) {
+    f(i) catch(e) { print(e) } cleanup { print("cleanup") }
+    i = i + 1
+  }
+}
+