Added npm run dev (#1572)

pyscript.core/dev.cjs

@@ -0,0 +1,33 @@
+let queue = Promise.resolve();
+
+const { exec } = require("node:child_process");
+
+const build = (fileName) => {
+    if (fileName) console.log(fileName, "changed");
+    else console.log("building without optimizations");
+    queue = queue.then(
+        () =>
+            new Promise((resolve, reject) => {
+                exec(
+                    "npm run rollup:xworker && npm run rollup:core && npm run rollup:pyscript",
+                    { cwd: __dirname, env: { ...process.env, NO_MIN: true } },
+                    (error) => {
+                        if (error) reject(error);
+                        else
+                            resolve(
+                                console.log(fileName || "", "build completed"),
+                            );
+                    },
+                );
+            }),
+    );
+};
+
+const options = {
+    ignored: /\/(?:__template|interpreters|xworker)\.[mc]?js$/,
+    persistent: true,
+};
+
+require("chokidar").watch("./esm", options).on("change", build);
+
+build();