chore: simplify package exports, enable tsdown exports, and upgrade to TypeScript 7

- Delegate `exports` map generation to tsdown (`exports: true`) and simplify `package.json` to a bare `"." : "./dist/index.mjs"` entry plus `"./package.json"`; drop redundant `main`/`module` fields
- Add `sideEffects: false` to `package.json` so bundlers can tree-shake the package
- Enable `clean: true` and `failOnWarn: true` in `tsdown.config.ts` for a cleaner build and stricter warning enforcement
- Suppress the TypeScript 7.0 experimental-API warning emitted by tsdown
- Bump `typescript` dev dependency to `^7.0.2`

package.json

@@ -31,15 +31,11 @@
     "dist"
   ],
   "type": "module",
-  "main": "./dist/index.mjs",
-  "module": "./dist/index.mjs",
+  "sideEffects": false,
   "types": "./dist/index.d.mts",
   "exports": {
-    ".": {
-      "types": "./dist/index.d.mts",
-      "import": "./dist/index.mjs",
-      "default": "./dist/index.mjs"
-    }
+    ".": "./dist/index.mjs",
+    "./package.json": "./package.json"
   },
   "publishConfig": {
     "access": "public"
@@ -59,12 +55,12 @@
     "tldts": "~7.4.13"
   },
   "devDependencies": {
-    "@types/node": "^26.6.1",
+    "@types/node": "^26.6.2",
     "oxfmt": "^0.68.0",
     "oxlint": "^1.83.0",
     "oxlint-tsgolint": "^7.0.2002",
     "tsdown": "^0.23.0",
-    "typescript": "^6.0.3",
+    "typescript": "^7.0.2",
     "vite": "^8.3.0",
     "vitest": "^5.0.1"
   },