Set frame values in multiple processes

[annehaley]

Setting values in multiple processes doesn't appear in the final result. That is, I think only the last process to write the zarr sets values.

Originally posted by @manthey in #1625 (comment)

To resolve this issue, we likely need to update the metadata upon every call to addTile, rather than only upon write. Resolving this issue should include writing a new test case for this behavior.