Add Thrift interpreter RPC contract tests

[jongyoul]

What is this PR for?

This is the first test-only slice (G-01A) of the Server-Interpreter RPC migration work.

The existing RemoteInterpreterServerTest calls the service implementation directly. This PR adds a real Thrift wire characterization test using TSocket, TBinaryProtocol, the generated client, and the generated processor.

It freezes these current control-plane behaviors:

• init/create/duplicate-create, form type, completion-driven lazy open, interpret, and close
• a 1 MiB interpret payload
• concurrent RUNNING status, manual progress, and cancel delivery over a second client connection
• execution errors returned in the result envelope
• declared InterpreterRPCException failures kept distinct from a raw Thrift transport failure

This PR does not change production code or behavior. It intentionally characterizes the current Thrift path; it is not yet the transport-neutral harness that later gRPC tests will use.

Out of scope for this slice: callback/event RPCs, pooled-client retry and deadlines, shutdown ambiguity, recovery, Angular/resource/application/library operations, and the legacy open RPC that currently has no production caller.

What type of PR is it?

Improvement

Todos

• Add deterministic automated coverage for the current Thrift control plane
• Run the complete zeppelin-interpreter test suite
• Link the parent Epic and child JIRA before marking this PR ready

What is the Jira issue?

TBD. This is kept as a draft until the planned RPC migration Epic and G-01A child issue are assigned. No JIRA issue was created or modified as part of this PR.

How should this be tested?

./mvnw test -pl zeppelin-interpreter \
  -Dtest=RemoteInterpreterServiceContractTest \
  -Dmaven.gitcommitid.skip=true

./mvnw test -pl zeppelin-interpreter \
  -Dmaven.gitcommitid.skip=true

./mvnw -pl zeppelin-interpreter checkstyle:check \
  -DskipTests \
  -Dmaven.gitcommitid.skip=true \
  -Dcheckstyle.includes='**/RemoteInterpreterServiceContractTest.java'

./mvnw -pl zeppelin-interpreter \
  org.apache.rat:apache-rat-plugin:check \
  -Prat -DskipTests -Dmaven.gitcommitid.skip=true

Local results:

• contract tests: 3 passed
• zeppelin-interpreter module: 129 passed
• Checkstyle for the new file: 0 violations
• RAT: 0 unapproved licenses

Screenshots (if appropriate)

Not applicable.

Questions:

• License files do not need an update; this PR adds test source only.
• There are no production or compatibility changes.
• User-facing documentation is not needed for this test-only slice.