This PR implements a test suite for ZIOApp that verifies proper finalizer execution and graceful shutdown behavior. It includes:

• Process-based testing utilities for launching and controlling ZIOApp instances
• Test cases for normal completion, finalizer execution, and signal handling
• Verification of nested finalizer execution order
• Timeout behavior testing for graceful shutdown
• Tests for race conditions between finalizers and JVM shutdown hooks
• Cross-platform signal handling with appropriate platform-specific isolation

Fixes #9909, addressing the issues identified in #9901, #9807, and #9240. /claim #9909