Use XDG_RUNTIME_DIR for config file instead of writing next to eslint's
package.json, which is root-owned in system-wide installs.

--- a/lib/config.js
+++ b/lib/config.js
@@ -1,5 +1,7 @@
 import debug from 'debug';
 import fs from 'node:fs/promises';
+import { mkdirSync } from 'node:fs';
+import { join } from 'node:path';

 const log = debug('eslint_d:config');

@@ -63,5 +65,9 @@ export async function removeConfig(resolver) {
  * @returns {string}
  */
 export function configFile(resolver) {
-  return `${resolver.base}/.eslint_d`;
+  const dir = process.env.XDG_RUNTIME_DIR
+    ? join(process.env.XDG_RUNTIME_DIR, 'eslint_d')
+    : join(process.env.HOME || '/tmp', '.cache', 'eslint_d');
+  mkdirSync(dir, { recursive: true });
+  return join(dir, `.eslint_d_${Buffer.from(resolver.base).toString('base64url')}`);
 }