Unable to save Duration tensors to Parquet

[sydduckworth]

arrow-rs doesn't support converting Duration arrays to/from Parquet format. To get around this, Synapse uses a hack where Duration arrays are cast to int64 before writing to disk, and when reading from disk a Cast node is inserted into the execution plan to convert back to duration.

This works for scalar arrays, but not for Duration tensors, which are represented as fixed-size lists, since the arrow-rs cast method doesn't support fixed-sized lists.

This should be fixed upstream in the near future since there is significant work being done in datafusion to better support fixed-size lists:
apache/datafusion#6560

In the meantime only scalar Duration fields are supported.