Fix selectSparkVersion() to use contains() instead of equals()

The current implementation of selectSparkVersion() was broken when sparkVersion
is supplied. The code was requiring an exact match instead of using contains(),
which never matched real Databricks Runtime version names like "12.2 LTS
(includes Apache Spark 3.3.2, Scala 2.12)".

This change aligns the Java SDK with the Go and Python SDK implementations,
which both use contains()/in operations for sparkVersion matching.

Fixes the issue described in PR #229.

Added comprehensive unit tests covering:
- Successful spark version matching with realistic API response data
- Multiple matches with latest=true/false behavior
- Integration with other selector parameters (ML, etc.)
- Error cases for non-existent versions

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: mgyucht

databricks-sdk-java/src/main/java/com/databricks/sdk/mixin/ClustersExt.java

@@ -50,7 +50,7 @@ public String selectSparkVersion(SparkVersionSelector selector) throws IllegalAr
         matches = version.getName().contains("LTS") || version.getKey().contains("-esr-");
       }
       if (matches && selector.sparkVersion != null) {
-        matches = ("Apache Spark " + selector.sparkVersion).equals(version.getName());
+        matches = version.getName().contains("Apache Spark " + selector.sparkVersion);
       }
       if (matches) {
         versions.add(version.getKey());

databricks-sdk-java/src/test/java/com/databricks/sdk/mixin/ClustersExtTest.java

@@ -1,6 +1,7 @@
 package com.databricks.sdk.mixin;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import com.databricks.sdk.core.ApiClient;
 import com.databricks.sdk.core.DatabricksConfig;
@@ -118,4 +119,86 @@ void nullComparisonTest() {
     String nodeType = clustersExt.selectNodeType(new NodeTypeSelector().withLocalDisk());
     assertEquals("testId1", nodeType);
   }
+
+  private GetSparkVersionsResponse testGetSparkVersionsWithSparkVersion() {
+    Collection<SparkVersion> versions = new ArrayList<>();
+    // Mock realistic Databricks Runtime versions based on actual API response format
+    versions.add(new SparkVersion()
+        .setName("12.2 LTS (includes Apache Spark 3.3.2, Scala 2.12)")
+        .setKey("12.2.x-scala2.12"));
+    versions.add(new SparkVersion()
+        .setName("13.3 LTS (includes Apache Spark 3.4.1, Scala 2.12)")
+        .setKey("13.3.x-scala2.12"));
+    versions.add(new SparkVersion()
+        .setName("14.3 LTS (includes Apache Spark 3.5.0, Scala 2.12)")
+        .setKey("14.3.x-scala2.12"));
+    versions.add(new SparkVersion()
+        .setName("14.2 ML (includes Apache Spark 3.5.0, Scala 2.12)")
+        .setKey("14.2.x-cpu-ml-scala2.12"));
+    // Add another version with same Spark version to create multiple matches
+    versions.add(new SparkVersion()
+        .setName("14.1 (includes Apache Spark 3.5.0, Scala 2.12)")
+        .setKey("14.1.x-scala2.12"));
+    return new GetSparkVersionsResponse().setVersions(versions);
+  }
+
+  @Test
+  void sparkVersionWithSparkVersionParameter() {
+    ClustersExt clustersExt = new ClustersExt(clustersMock);
+    Mockito.doReturn(testGetSparkVersionsWithSparkVersion()).when(clustersMock).sparkVersions();
+    
+    // Test exact spark version match
+    String sparkVersion = clustersExt.selectSparkVersion(
+        new SparkVersionSelector().withSparkVersion("3.4.1"));
+    assertEquals("13.3.x-scala2.12", sparkVersion);
+  }
+
+  @Test
+  void sparkVersionWithSparkVersionParameterMultipleMatches() {
+    ClustersExt clustersExt = new ClustersExt(clustersMock);
+    Mockito.doReturn(testGetSparkVersionsWithSparkVersion()).when(clustersMock).sparkVersions();
+    
+    // Test spark version with multiple matches - should return latest when latest=true is explicitly set
+    String sparkVersion = clustersExt.selectSparkVersion(
+        new SparkVersionSelector().withSparkVersion("3.5.0").withLatest());
+    // Should return the highest version (14.3.x) when latest=true and multiple 3.5.0 versions match
+    assertEquals("14.3.x-scala2.12", sparkVersion);
+  }
+
+  @Test
+  void sparkVersionWithSparkVersionParameterAndML() {
+    ClustersExt clustersExt = new ClustersExt(clustersMock);
+    Mockito.doReturn(testGetSparkVersionsWithSparkVersion()).when(clustersMock).sparkVersions();
+    
+    // Test spark version combined with ML requirement
+    String sparkVersion = clustersExt.selectSparkVersion(
+        new SparkVersionSelector().withSparkVersion("3.5.0").withML());
+    assertEquals("14.2.x-cpu-ml-scala2.12", sparkVersion);
+  }
+
+  @Test
+  void sparkVersionWithSparkVersionParameterNoMatch() {
+    ClustersExt clustersExt = new ClustersExt(clustersMock);
+    Mockito.doReturn(testGetSparkVersionsWithSparkVersion()).when(clustersMock).sparkVersions();
+    
+    // Test spark version that doesn't exist
+    assertThrows(IllegalArgumentException.class, () -> {
+      clustersExt.selectSparkVersion(
+          new SparkVersionSelector().withSparkVersion("2.4.5"));
+    });
+  }
+
+  @Test
+  void sparkVersionWithSparkVersionParameterMultipleMatchesLatestFalse() {
+    ClustersExt clustersExt = new ClustersExt(clustersMock);
+    Mockito.doReturn(testGetSparkVersionsWithSparkVersion()).when(clustersMock).sparkVersions();
+    
+    // Test spark version with multiple matches and latest=false (default) - should throw exception
+    SparkVersionSelector selector = new SparkVersionSelector().withSparkVersion("3.5.0");
+    // latest defaults to false, so multiple matches should throw an exception
+    
+    assertThrows(IllegalArgumentException.class, () -> {
+      clustersExt.selectSparkVersion(selector);
+    }, "Expected exception when multiple versions match with latest=false (default)");
+  }
 }