deduplication when combining processing/QC records

We need to support combination/adding/aggregation of QC and processing records when creating metadata for later stages of processing, but right now when those records are combined there is no check that duplicate records are not getting created. Duplicates will happen for a processing graph like
```
A--B--D
\-C-/
```
We should add some simple logic that checks and removes duplicates based on processing/QC record creation datetime.