Don't reuse closed or mismatched MariaDB clients

grabMariaDBClient reused global.MARIADB_CLIENT whenever the requested
config matched global.CONFIG. It never checked that the client was made
from that config or was still open. init() sets global.CONFIG before
creating the client, so a re-init after a close, or a config change, got
back a closed or wrong client.

- Remember the cache key each client was created with, and compare that
- Wrapping close() drops the client from the cache and unsets
  global.MARIADB_CLIENT, so the next grab or ensureInit makes a new one
- resolveClient goes through grabMariaDBClient instead of repeating the
  global.CONFIG comparison
- Remove the queue test's workaround for this

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tests/queue.test.ts

@@ -52,20 +52,10 @@ describe.skipIf(!TEST_DB)("Queue tables", () => {
         const createDBSchema = (await import("../src/lib/schema/create-db-schema")).default;
         const appendDefaults = (await import("../src/utils/append-default-fields-to-db-schema")).default;
 
-        /**
-         * The test container uses a self-signed certificate. `db_config` gives
-         * this file its own client, since other test files close theirs. The
-         * client is created before `global.CONFIG` changes, so the previous
-         * file's closed global client isn't reused.
-         */
-        const config = {
-            db_name: TEST_DB!,
-            ssl_reject_unauthorized: false,
-            db_config: { max: 10 },
-        };
-        setMariaDBClient({ config });
-        global.CONFIG = config;
+        // The test container uses a self-signed certificate
+        global.CONFIG = { db_name: TEST_DB!, ssl_reject_unauthorized: false };
         global.DB_SCHEMA = schema;
+        setMariaDBClient({ config: global.CONFIG });
 
         DB = (await import("../src/index")).default;