[SPARK-52073] Add pi example

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to add pi example.

Why are the changes needed?

This is a Swift Pi example corresponding to SparkDataFramePi.scala.

• https://github.com/apache/spark/blob/master/examples/src/main/scala/org/apache/spark/examples/sql/SparkDataFramePi.scala

$ swift run SparkConnectSwiftPi 1000000
...
Connected to Apache Spark 4.0.0 Server
Pi is roughly 3.1423711423711422

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Manual review.

Was this patch authored or co-authored using generative AI tooling?

No.

[dongjoon-hyun]

Let me merge this new example to move forward.