[ZEPPELIN-6548] Use specific exceptions for Spark Scala fallback detection

[miinhho]

What is this PR for?

This PR refines exception types in SparkInterpreterLauncher when the fallback Spark Scala version detection validates the SPARK_HOME/jars layout.

Previously, detectSparkScalaVersionByReplClass(...) threw generic Exception for expected validation failures such as missing or duplicate spark-repl jars, or an unsupported spark-repl Scala suffix. This PR replaces those generic throw sites with more specific exception types while keeping the existing messages and caller behavior unchanged.

Missing or duplicate spark-repl jars now throw IOException, and an unrecognized Scala suffix now throws IllegalArgumentException.

This PR is a follow-up to ZEPPELIN-6464

What type of PR is it?

Improvement

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6548

How should this be tested?

• Build and run the module tests:

./mvnw test -pl zeppelin-server --am

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No