feat: migrate to ESM-only build

Switches the build setup to only output ESM now that `require(esm)` is a
thing.

Author: 43081j

Diff for: package.json

@@ -5,10 +5,7 @@
   "description": "A minimal library for executing processes in Node",
   "main": "./dist/main.js",
   "files": [
-    "dist",
-    "!dist/node_modules",
-    "!dist/cjs/test",
-    "!dist/esm/test"
+    "dist"
   ],
   "scripts": {
     "build": "npm run build:types && tsup",
@@ -54,10 +51,6 @@
       "import": {
         "types": "./dist/main.d.ts",
         "default": "./dist/main.js"
-      },
-      "require": {
-        "types": "./dist/main.d.cts",
-        "default": "./dist/main.cjs"
       }
     },
     "./package.json": "./package.json"

Diff for: tsup.config.ts

@@ -3,7 +3,7 @@ import { defineConfig } from "tsup";
 export default defineConfig({
   entryPoints: ["src/main.ts"],
   outDir: "dist",
-  format: ["esm", "cjs"],
+  format: ["esm"],
   tsconfig: "./tsconfig.json",
   target: "es2022",
   minify: false,