chore: use .mjs for rollup config to instruct Rollup to treat it as a…

… pure ES module

rollup.config.mjs

@@ -0,0 +1,58 @@
+import ts from "rollup-plugin-ts";
+import pkg from "./package.json" assert {type: "json"};
+import {builtinModules} from "module";
+
+const SHARED_OPTIONS = {
+	plugins: [
+		ts({
+			tsconfig: "tsconfig.build.json"
+		})
+	],
+	external: [
+		...builtinModules,
+		...Object.keys(pkg.dependencies),
+		...Object.keys(pkg.devDependencies),
+		...Object.keys(pkg.peerDependencies)
+	]
+};
+
+const SHARED_OUTPUT_OPTIONS = {
+	sourcemap: true,
+	hoistTransitiveImports: false,
+	generatedCode: "es2015",
+	compact: false,
+	minifyInternalExports: false
+};
+
+
+export default [
+	{
+		input: "src/index.ts",
+		preserveEntrySignatures: true,
+		output: [
+			{
+				file: pkg.exports.require,
+				format: "cjs",
+				...SHARED_OUTPUT_OPTIONS
+			},
+			{
+				file: pkg.exports.import,
+				format: "esm",
+				...SHARED_OUTPUT_OPTIONS
+			}
+		],
+		...SHARED_OPTIONS
+	},
+	{
+		input: "src/cli/index.ts",
+		preserveEntrySignatures: true,
+		output: [
+			{
+				dir: "./dist/cli",
+				format: "esm",
+				...SHARED_OUTPUT_OPTIONS
+			}
+		],
+		...SHARED_OPTIONS
+	}
+];