Investigate why test fixtures go :boom: if we have more than one TEST in a single process.

[arjo129]

Google protobuf doesn't like the way we are linking the messages in our repository. Whenever we try to run two TestFixtures in the same process the tests will segfault.

[hidmic]

protocolbuffers/protobuf#4126 suggests loading/unloading protobuf message shared libraries leaves bad global state behind. Perhaps we can preload them?

[arjo129]

Hopefully eventually we can move away from custom messages then?

[marcoag]

In general running two servers in the same test seems to be troublesome with gazebo. Dunno if its the same issue but I also had troubles trying to run two servers in the same test file in gz-sim so I have to split them in two files (here and here).

[hidmic]

We know why this happens and it's very much core to how protobuf works. I'm inclined to close this as wont fix.