fix(cu): return previous assignment evaluation on duplicate

[jfrain99]

Background

In the CU, when a duplicate assignment is received in the eval stream (that is, an assignment of a tx that has been previously assigned), the CU currently does some work and removes this evaluation from the eval stream.

Problem

This is non-optimal, as the work being done can be avoided.

Proposed Solution

Before initializing our eval stream (in the function maybeExactEval, search the evaluations sqlite table by processId and messageId to find previous instance of this assignment. If it exists, return the result of the previous evaluation and continue.