Add cleanup function for SITL Gazebo on macOS

[farhangnaderi]

Solved Problem

When running PX4 SITL on macOS, pressing Ctrl+C would not always cleanly stop the simulation processes (e.g., gz sim). This often forced users to press Ctrl+C multiple times or manually kill processes.

Solution

• Added a cleanup() function guarded by if [ "$(uname)" = "Darwin" ].
• Within cleanup(), use pkill -f "gz sim" || true to stop Gazebo simulation processes.
• Clear the trap for INT TERM signals right before exit 0.

Changelog Entry

For release notes:

New Gazebo Harmonic SITL on MacOS 

Alternatives

We could also add a kill 0 call or a broader signal handling mechanism, but pkill -f "gz sim" suffices for macOS SITL with minimal side effects.

Test coverage

• Local testing on macOS Sequoia.

Context

N/A

I cannot add reviewers here. @mrpollo @MaEtUgR @ThomasDebrunner you might want to try.

[DronecodeBot]

This pull request has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-sync-q-a-dec-18-2024/42886/1