Move interprocess examples to zeromq subdirectory and add UDPM basic publisher/subscriber examples

[Copilot]

Summary

This PR reorganizes the interprocess examples and adds new UDP Multicast (UDPM) transport examples.

Changes

Reorganization:

• Moves all existing examples from src/interprocess/ to src/interprocess/zeromq/ (basic_publisher, basic_subscriber, gps_driver, hold, json, log_control, mavlink, state_machine)
• Moves all launch and deployment files from launch/interprocess/ to launch/interprocess/zeromq/
• Updates the top-level CMakeLists.txt deployment figure paths accordingly

New UDPM Examples:

• Adds src/interprocess/udpm/basic_publisher/ — equivalent to the zeromq basic publisher but uses goby::udpm::SingleThreadApplication (no central gobyd daemon needed)
• Adds src/interprocess/udpm/basic_subscriber/ — equivalent to the zeromq basic subscriber
• Adds launch/interprocess/udpm/basic_publisher_subscriber.launch — no gobyd entry needed for UDPM
• Adds launch/interprocess/udpm/basic_publisher_subscriber_deployment.yml

CMake:

• New src/interprocess/CMakeLists.txt always builds the zeromq subdirectory and conditionally builds udpm if goby/udpm/protobuf/interprocess_config.proto is found (requires goby >= 3.3.1+49 with UDPM transport merged)

Documentation:

• Updates README.md to document both the zeromq and udpm basic pub/sub examples with updated paths

Notes

The UDPM examples require the goby3 UDPM transport headers (merged into goby3 master at commit 0cbdf6f0 on 2026-03-25). The build will emit a cmake warning and skip the udpm examples if these headers are not yet available in the installed libgoby3-dev package; the CI uses dist-upgrade from the continuous PPA which will pick up the new package once it's built.