[SPARK-56374][BUILD] Add missing Arrow shade rule to SBT Connect client assembly

Add org.apache.arrow relocation to SparkConnectClient (jvm) and
SparkConnectJdbc assembly shade rules in SparkBuild.scala, matching
Maven's client pom.xml.

Maven shades Arrow classes to org/sparkproject/org/apache/arrow/ in
the Connect client JAR. SBT was missing this rule, leaving 998 Arrow
classes unshaded at org/apache/arrow/ inside the assembly JAR.

This is a small incremental step toward full SBT/Maven assembly
parity (SPARK-56374). The Connect server assembly already matches
Maven (identical class count and shaded namespaces). Other gaps
(extra unshaded transitive dependencies in SBT client JARs,
network-yarn native library renaming, CopyDependencies) are left
for follow-up work.

Author: Anupam Yadav

project/SparkBuild.scala

@@ -926,6 +926,7 @@ object SparkConnectJdbc {
       ShadeRule.rename("io.netty.**" -> "org.sparkproject.connect.client.io.netty.@1").inAll,
       ShadeRule.rename("io.perfmark.**" -> "org.sparkproject.connect.client.io.perfmark.@1").inAll,
       ShadeRule.rename("org.codehaus.**" -> "org.sparkproject.connect.client.org.codehaus.@1").inAll,
+      ShadeRule.rename("org.apache.arrow.**" -> "org.sparkproject.connect.client.org.apache.arrow.@1").inAll,
       ShadeRule.rename("android.annotation.**" -> "org.sparkproject.connect.client.android.annotation.@1").inAll
     ),
 
@@ -1007,6 +1008,7 @@ object SparkConnectClient {
       ShadeRule.rename("io.netty.**" -> "org.sparkproject.connect.client.io.netty.@1").inAll,
       ShadeRule.rename("io.perfmark.**" -> "org.sparkproject.connect.client.io.perfmark.@1").inAll,
       ShadeRule.rename("org.codehaus.**" -> "org.sparkproject.connect.client.org.codehaus.@1").inAll,
+      ShadeRule.rename("org.apache.arrow.**" -> "org.sparkproject.connect.client.org.apache.arrow.@1").inAll,
       ShadeRule.rename("android.annotation.**" -> "org.sparkproject.connect.client.android.annotation.@1").inAll
     ),