[SPARK-45429][CORE] Add helper classes for SSL RPC communication

[hasnain-db]

What changes were proposed in this pull request?

This PR adds helper classes for SSL RPC communication that are needed to work around the fact that netty does not support zero-copy transfers.

These mirror the existing MessageWithHeader and MessageEncoder classes with very minor differences. But the differences were just enough that it didn't seem easy to refactor/consolidate, and since we don't expect these classes to change much I hope it's ok.

Why are the changes needed?

These are needed to support transferring ManagedBuffers into a form that can be transferred by netty over the network, since netty's encryption support does not support zero-copy transfers.

Does this PR introduce any user-facing change?

No

How was this patch tested?

Added unit tests

build/sbt
> project network-common
> testOnly org.apache.spark.network.protocol.EncryptedMessageWithHeaderSuite

The rest of the changes and integration were tested as part of #42685

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

No

[mridulm]

While waiting for tests, please fix the nit as well.
It wont impact the test result anyway

[hasnain-db]

org.apache.spark.sql.kafka010.KafkaSourceStressSuite is failing on this and the other outstanding PR, and seems to be unrelated to the changes here. I wonder if that is related to the new kafka version bump since it looks like it also failed on https://github.com/apache/spark/actions/runs/6497942586/job/17648192318

[mridulm]

Can you retrigger the tests please ? There are a bunch of failures.

[hasnain-db]

done, will re-request review once failures are minimized

[hasnain-db]

@mridulm I believe the only failure now is org.apache.spark.sql.kafka010.KafkaSourceStressSuite

[mridulm]

There was a failure in KafkaSourceStressSuite, which is unrelated to this PR.
Merged to master.

Thanks for working on this @hasnain-db !