Add serverless Scala JAR job example

[imran-a-hasan]

A minimal, self-contained Scala JAR job that runs on Databricks serverless compute, packaged as a Databricks Asset Bundle. It's meant as a copy-and-go starting point — the bundle builds the JAR with sbt assembly, uploads it, and defines a serverless JAR job.

The example demonstrates three basic building blocks:

• Spark basics — get the session, build a DataFrame, read a Unity Catalog table (samples.nyctaxi.trips).
• UDF basics — scalar, map-returning, SQL-registered, and a UDF closing over a locally-defined class (exercises closure serialization).
• dbutils basics — the job/notebook context and a dbutils.fs read/write round-trip against a UC volume.

Serverless specifics it follows: Spark Connect session via SparkSession.builder().getOrCreate() (no SparkContext/RDD), builds against databricks-connect + databricks-dbutils-scala (both % provided), targets Scala 2.13.16 / JDK 17, serverless environment client: "5".

Deploy: databricks bundle deploy -t dev then databricks bundle run -t dev serverless-jar-job-example. Verified end-to-end on serverless — the run completes with ServerlessJarJobExample: all examples completed successfully.

See serverless-jar-job-example/README.md for full docs.

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