Fix differences duplication in dict compare

[Dykam]

.VisitingIndex makes a copy of the entire context, which then gets merged with the same original context, duplicating the Differences. In case a difference was detected at the start of a dictionary, you end up with 2^keys amount of duplicate differences.

Fix this by creating a new empty context for the inner comparison.

[evdkramer]

Wow we had weeks of stress because of this bug. Highly encourage this PR to be merged

[jamesfoster]

Thanks for the report. Fixed in 4.0.0