Remove tests related module from Hex

[SimonLab]

I think we can remove at least the mocks module from hex.
I would maybe just left the Gogs module as it is the only one used when the package is installed on other project.

I think we can also convert some function to private functions. This will reduce the number of function in the public api

[nelsonic]

@SimonLab I actually think these are useful for people to understand how the internals work for the mocks.
But agree that we could exclude them from the Hex Docs to not overwhelm people with functions that they aren't going to use. 💭