Handler has been introduced to listen for messages through IPC, and be able to relay messages through IPC.
The handler is returned from spinning up the child process via Rust Command, which means this code will be reusable for future tests.
handling_test_info will always be used at the start of any test, to obtain the correct Chronik URL for testing, therefore we abstract
this into its own function. MPSC channels are used to communicate between the main thread and the handler loop.

Please set BUILD_DIR env to export BUILD_DIR="/path/to/build_dir
UNIX: ./contrib/teamcity/build-configurations.py build-bitcoinsuite-chronik-client
To ensure no breaking changes from the updated IPC file, run ./contrib/teamcity/build-configurations.py chronik-client-integration-tests from bitcoin-abc to run typescript tests.