switch to tsup for build

package.json

···
 		"format": "biome format --write ./src",
 		"test": "vitest --run",
 		"lex-gen": "lex gen-api ./src/leaflet/lexicons ./lexicons/pub/leaflet/* ./lexicons/pub/leaflet/*/* ./lexicons/com/atproto/*/* --yes",
-		"typecheck": "tsc --noEmit",
-		"build": "rm -rf dist && tsc"
+		"typecheck": "tsc",
+		"build": "rm -rf dist && tsup"
 	},
 	"license": "MIT",
 	"files": [
···
 	],
 	"type": "module",
 	"main": "dist/index.js",
+	"exports": {
+		".": {
+			"import": "./dist/index.js",
+			"require": "./dist/index.cjs"
+		}
+	},
 	"devDependencies": {
 		"@atproto/lex-cli": "^0.9.1",
 		"@biomejs/biome": "2.1.3",

tsconfig.json

···
 		"moduleResolution": "bundler",
 		"rootDir": "src",
 		"sourceMap": true,
+		"noEmit": true,
 		"declaration": true
 	},
 	"include": ["./src"],

tsup.config.ts

···
+import { defineConfig } from "tsup";
+
+export default defineConfig({
+	entryPoints: ["src/index.ts"],
+	format: ["cjs", "esm"],
+	dts: true,
+	outDir: "dist",
+	clean: true,
+});