feat: make java client builder generic (#2851)

In #2845 we ported the lancedb integration in lance-namespace to
lancedb. But that is too specific to RestNamespace. We can improve the
user entry point so that we can put local mode and future version of the
Flight SQL-based LanceDB server all behind this single
`LanceDbNamespaceClientBuilder` API.

Also I renamed `namespace` to `namesapceClient` to avoid confusion with
the namespace path.

java/lancedb-core/src/test/java/com/lancedb/LanceDbNamespaceClientBuilderTest.java

@@ -17,13 +17,13 @@ import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.*;
 
-/** Unit tests for LanceDbRestNamespaceBuilder. */
-public class LanceDbRestNamespaceBuilderTest {
+/** Unit tests for LanceDbNamespaceClientBuilder. */
+public class LanceDbNamespaceClientBuilderTest {
 
   @Test
   public void testBuilderRequiresApiKey() {
-    LanceDbRestNamespaceBuilder builder =
-        LanceDbRestNamespaceBuilder.newBuilder().database("test-db");
+    LanceDbNamespaceClientBuilder builder =
+        LanceDbNamespaceClientBuilder.newBuilder().database("test-db");
 
     IllegalStateException exception = assertThrows(IllegalStateException.class, builder::build);
     assertEquals("API key is required", exception.getMessage());
@@ -31,8 +31,8 @@ public class LanceDbRestNamespaceBuilderTest {
 
   @Test
   public void testBuilderRequiresDatabase() {
-    LanceDbRestNamespaceBuilder builder =
-        LanceDbRestNamespaceBuilder.newBuilder().apiKey("test-api-key");
+    LanceDbNamespaceClientBuilder builder =
+        LanceDbNamespaceClientBuilder.newBuilder().apiKey("test-api-key");
 
     IllegalStateException exception = assertThrows(IllegalStateException.class, builder::build);
     assertEquals("Database is required", exception.getMessage());
@@ -43,7 +43,7 @@ public class LanceDbRestNamespaceBuilderTest {
     IllegalArgumentException exception =
         assertThrows(
             IllegalArgumentException.class,
-            () -> LanceDbRestNamespaceBuilder.newBuilder().apiKey(null));
+            () -> LanceDbNamespaceClientBuilder.newBuilder().apiKey(null));
     assertEquals("API key cannot be null or empty", exception.getMessage());
   }
 
@@ -52,7 +52,7 @@ public class LanceDbRestNamespaceBuilderTest {
     IllegalArgumentException exception =
         assertThrows(
             IllegalArgumentException.class,
-            () -> LanceDbRestNamespaceBuilder.newBuilder().apiKey("  "));
+            () -> LanceDbNamespaceClientBuilder.newBuilder().apiKey("  "));
     assertEquals("API key cannot be null or empty", exception.getMessage());
   }
 
@@ -61,7 +61,7 @@ public class LanceDbRestNamespaceBuilderTest {
     IllegalArgumentException exception =
         assertThrows(
             IllegalArgumentException.class,
-            () -> LanceDbRestNamespaceBuilder.newBuilder().database(null));
+            () -> LanceDbNamespaceClientBuilder.newBuilder().database(null));
     assertEquals("Database cannot be null or empty", exception.getMessage());
   }
 
@@ -70,14 +70,14 @@ public class LanceDbRestNamespaceBuilderTest {
     IllegalArgumentException exception =
         assertThrows(
             IllegalArgumentException.class,
-            () -> LanceDbRestNamespaceBuilder.newBuilder().database("  "));
+            () -> LanceDbNamespaceClientBuilder.newBuilder().database("  "));
     assertEquals("Database cannot be null or empty", exception.getMessage());
   }
 
   @Test
   public void testBuilderFluentApi() {
     // Verify the builder returns itself for chaining
-    LanceDbRestNamespaceBuilder builder = LanceDbRestNamespaceBuilder.newBuilder();
+    LanceDbNamespaceClientBuilder builder = LanceDbNamespaceClientBuilder.newBuilder();
 
     assertSame(builder, builder.apiKey("test-key"));
     assertSame(builder, builder.database("test-db"));
@@ -88,8 +88,8 @@ public class LanceDbRestNamespaceBuilderTest {
 
   @Test
   public void testNewBuilderCreatesNewInstance() {
-    LanceDbRestNamespaceBuilder builder1 = LanceDbRestNamespaceBuilder.newBuilder();
-    LanceDbRestNamespaceBuilder builder2 = LanceDbRestNamespaceBuilder.newBuilder();
+    LanceDbNamespaceClientBuilder builder1 = LanceDbNamespaceClientBuilder.newBuilder();
+    LanceDbNamespaceClientBuilder builder2 = LanceDbNamespaceClientBuilder.newBuilder();
 
     assertNotSame(builder1, builder2);
   }