Replaced tsconfig.build.json with tsdown configuration for simplified builds.

tsdown.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from "tsdown";
+
+export default defineConfig({
+  entry: ["src/index.ts"],
+  platform: "node",
+  dts: true,
+  external: ["psl"],
+});