Bugfix/value pmob cast

[holtzman]

Motivation

The wallet database doesn't store u64s and full-service casts u64s to i64 for storage. In a few places, those values being retrieved from the database were not being cast back to u64 before being used, notably in transaction_log processing and receipt processing.

In this PR

• fixed two missing u64 casts in v1 transaction_log retrieval
• fixed a missing u64 cast when forming an response indicating that that a receipt's value doesn't match the txo.

[nick-mobilecoin]

looks good, there are a couple test cases left using i64, but they're also comparing to i64.
Very anecdotal, but this is a good argument for normalizing data before passing it around.