Add the ability to transform scan specs

[DominicOram]

It would be nice if scanspec had the ability to transform (particularly rotate) a whole scan. For example something like:

from scanspec import some_rotation_obj

my_rotation = some_rotation_obj(axis=x, deg=45)

# Something required to specify x, y and z are 90 deg from each other

original_grid = Line(y, 0.0, 1.0, 3) * ~Line(x, 0.0, 1.0, 3)
new_grid = original_grid * my_rotation
print(original_grid, new_grid)
...
# [{'y': 0.0, 'x': 0.0}, {'y': 0.0, 'x': 0.5}, {'y': 0.0, 'x': 1.0}, {'y': 0.5, 'x': 1.0} ...
# [{'y': 0.0, 'z': 0.0, 'x': 0.0}, {'y': 0.0, 'z': 0.0, 'x': 0.5}, {'y': 0.0, 'z': 0.0, 'x': 1.0}, {'y': 0.25, 'z': 0.25, 'x': 1.0} ...

I appreciate this would require scanspec having to know about the co-ordiante system it is in, which is a big addition so don't mind if it's outside of the scope for scanspec. However, it is something that we need to do some variation of a lot and can sometimes be a bit fiddly so having a central module do it would be helpful.