Pass 2: resolves parsed GNU unit expressions into numeric factors and dimension maps relative to SI primitives.

Each resolved unit becomes {factor, dimensions} where dimensions is a map of GNU primitive name to integer power. For example:

• foot → {0.3048, %{"m" => 1}}
• newton → {1.0, %{"kg" => 1, "m" => 1, "s" => -2}}

Resolution is recursive with memoization via the process dictionary to keep stack frames small during deep chains.