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/loop_if_join_postfix.nyash

@@ -0,0 +1,16 @@
+function f(x) {
+  return x
+}
+
+function main(args) {
+  local i = 0
+  local a = 0
+  loop(i < 2) {
+    // both branches assign to the same variable -> JoinResult(a)
+    if i % 2 == 0 { a = 1 } else { a = 2 }
+    // include postfix sugar to exercise TryCatch normalization in the same scope
+    with_cleanup(postfix_catch(f(i), "Error", fn(e){ print(e) }), fn(){ })
+    i = i + 1
+  }
+}
+