Unwrap side input from OutputRef before passing to memory estimator function

[yousefmoazzam]

Suppose a side input that is passed to a method is also involved in memory estimation (such as the overlap generated by find_center_360 being passed as a side input to sino_360_to_180).

Currently, the value will be passed to the memory estimator function wrapped inside an OutputRef, rather than passing the value itself. This results in:

• needing to unwrap the value from the OutputRef before using it in the memory estimator (not so bad)
• in a memory estimator test that has a method using a side input, one needs to mock an OutputRef whose value property is fixed to return the value (slightly more annoying)

It feels like it may be nicer to have memory estimator function receive the wrapped value rather than an OutputRef object, so then memory estimator functions don't need to know about OutputRef and can focus solely on memory calculations.