Account for hoisting in RotationCountVisitor

The RotationCountVisitor currently counts each shift in a multi-rotation op (e.g., LinearTransformOp) individually. When fast rotation precomputation (hoisting) is used, many of these rotations share intermediate results, so the actual cost is lower.

> Maybe the rotation visitor constructor can be configured to say "support fast rotation precompute" and then this cost would be some fraction of num_shifts instead.

_Originally posted by @j2kun in https://github.com/google/heir/pull/2818#discussion_r2997396747_