feat: better introspection for encumbered magnitude

[wadealexc]

Reasoning: current encumberedMagnitude is a public getter that returns the non-updated version of an operator's encumbered magnitude.

When actually calling modifyAllocations, we use the updated version -- so this is probably more relevant to expose.

This PR makes the encumberedMagnitude mapping internal, and instead exposes a getter (getEncumberedMagnitude) that returns the current encumbered magnitude with completable deallocations included.

[ypatil12]

LGTM, one non-blocking nit. Would also be good to have a test confirming expected behavior of the view func

[wadealexc]

LGTM, one non-blocking nit. Would also be good to have a test confirming expected behavior of the view func

So it doesn't really look like it because the updates I made to tests were very small, but the updated unit tests actually do check that the new function behaves correctly.

I was also planning to further dig into this in integration tests -- this version of getting encumbered magnitude makes integration test invariant/assertion writing much easier :)

[8sunyuan]

LGTM, the only code smell to me is how these view functions are implemented differently from the internal logic but thats been the case for a while. A bit late for a refactor.