fix: declare IOException in tearDown for Spark 4.x compile

`SparkSession.close()` throws checked `IOException` on Spark 4.x but
not on 3.x. The base test file is added to every version module's test
source set, so the missing `throws` clause broke `make test` on Spark
4.0/4.1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Vova Kolmakov

lance-spark-base_2.12/src/test/java/org/lance/spark/read/BaseLanceVectorSearchTest.java

@@ -75,7 +75,7 @@ public void setup() throws IOException {
   }
 
   @AfterEach
-  public void tearDown() {
+  public void tearDown() throws IOException {
     if (spark != null) {
       spark.close();
       spark = null;