build(tooling): modernize Node and TypeScript setup

tsup.config.ts

@@ -3,7 +3,12 @@ import { defineConfig } from 'tsup';
 export default defineConfig({
     format: ['cjs', 'esm'],
     entry: ['./src/index.ts'],
-    dts: false,
+    dts: {
+        compilerOptions: {
+            // tsup's declaration bundler still sets the removed baseUrl option internally.
+            ignoreDeprecations: '6.0',
+        },
+    },
     shims: true,
     skipNodeModulesBundle: true,
     clean: true,