Ability to set GZ_DISCOVERY_* variables from the Python API

[AmalDevHaridevan]

Desired behaviour

Currently, for a single process, python interpreter doesn’t perform dlclose after opening any cython library until the process terminates. This produces issues when the variables have global visibility, which is the default for pybind. We can set visibility for these variables within only the objects scope by passing appropriate flags in the pybind module.

My specific problem has to do with the Node creation. I want to instantiate multiple Nodes in isolated network in a single process. Currently due to the mentioned problem, this is impossible because the Node will stay with the env vars found at first import. We cannot delete references to the module from sys.modules and obtain desired behaviour.

I would like to work on this as well, to contribute to the project.

Alternatives considered

Implementation suggestion

Additional context

Multiple isolated Nodes in a single Python process.