Replace tsup with tsdown

tsdown.config.ts

@@ -0,0 +1,19 @@
+import { defineConfig } from "tsdown";
+import packageJson from "./package.json" with { type: "json" };
+
+export default defineConfig((options) => {
+  const dev = !!options.watch;
+  return {
+    entry: ["src/**/*.(ts|js)"],
+    format: ["esm"],
+    target: "node24",
+    unbundle: true,
+    dts: true,
+    sourcemap: true,
+    clean: true,
+    splitting: false,
+    minify: !dev,
+    external: [...Object.keys(packageJson.peerDependencies), "dotenv"],
+    tsconfig: "tsconfig.json",
+  };
+});