re_datastore: generalized deduplication

[teh-cmc]

Generalized deduplication

• deduplicate across timelines across multiple calls

• automagically deduplicate within a single component table

• note: probably never worth doing in real-time, but can be interesting while serializing

[teh-cmc]

Interestingly, like computing cell sizes, this is one of these things that could be computed in the clients' batching threads (i.e. the hash of the cell's contents).

Another interesting tidbit: this is really not that different from the ongoing work regarding DataType deduplication (#1809).