Unchecked assumptions on attribute type

[bwohlberg]

This line implicitly assumes that A is a LinearOperator

scico/scico/loss.py

Line 195 in 2b7a693

rhs = v + 2 * lam * α * A.adj(W(y))

but according to the typing on the A parameter of the class __init__,

scico/scico/loss.py

Line 124 in 2b7a693

A: Optional[Union[Callable, operator.Operator]] = None,

A may also be a function, which does not have an adj method.

The prox method needs some additional checking to ensure that A is a LinearOperator, raising an exception if it is not.

[tbalke]

Good catch. I'll fix it