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`

tsdown.config.ts

@@ -4,7 +4,11 @@ export default defineConfig({
   platform: "node",
   target: "node20",
   entry: ["src/index.ts"],
+  clean: true,
   dts: true,
+  exports: true,
   nodeProtocol: "strip",
   deps: { neverBundle: ["tldts"] },
+  failOnWarn: true,
+  suppressWarnings: ["TypeScript 7.0 does not yet have a stable API and is experimental"],
 });