Efficient imports

[GarethCabournDavies]

In an attempt to remove "from xxx import *"-style imports from more places, I've used git grep import | grep "*" | grep -v css| grep -v __init__ to find any places where this is used.

I then commented out the import, ran the tests to find what needs importing and getting that explicitly (not the most sophisticated, but seems to have worked).

After this change there is now 1 place which uses "from xxx import *", which is the versioning module, and I think that is valid.

The changes are mainly in the test suite - I've tried as much as possible to get tests to now pass, using cpu and cuda schemes, as these were what was catered for before!

I'd like to have other schemes / backends working, and some cuda tests fail, but that is for another PR

Standard information about the request

This is a code quality change
This change affects: the offline search, the live search, inference, PyGRB

This change: has appropriate unit tests, follows style guidelines (See e.g. PEP8), has been proposed using the contribution guidelines

Motivation

#4783

Testing performed

Ran tests manually - they worked. The CI will also check this

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