Add common numpy transforms to extra_namespace

[tomicapretto]

Adds the following transformations

• log()
• log2()
• log10()
• exp()
• exp2()
• abs()

Previously

import numpy as np
model = bmb.Model("y ~ np.log(x)", data)

Now

model = bmb.Model("y ~ log(x)", data)

Closes #587

[tomicapretto]

I think the failing test is because pymc-devs/pymc#6291 in PyMC, which is included in the v4.4 release of PyMC. Will fix it in another PR but need to think about it since Bambi requests PyMC > 4 and this would bring problems with PyMC < 4.4