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/postfix_catch.nyash

@@ -0,0 +1,9 @@
+// Phase 1 sugar: postfix_catch(expr, "Error", fn(e){ body })
+function do_work(args) {
+  return 0
+}
+
+function main(args) {
+  postfix_catch(do_work(args), "Error", fn(e){ print(e) })
+}
+