Cache File and Dataset IDs for DataStubs

[lawrence-mbf]

• cache file and dataset ids on load and destroy them if possible.
• use a different solution for bound pipes which may cause file corruption if the dataset is not properly closed.

[lawrence-mbf]

Currently blocked by #448 (comment)

[ehennestad]

@lawrence-mbf

Is the idea here to keep h5 IDs in memory to avoid opening and closing files/datasets more times than needed?

[lawrence-mbf]

@ehennestad I believe this was because network drives were incredibly slow to process when opened/closed. Data processing is much faster if the file ids were kept open, though you would have to be diligent to maintain the file ids so you don't get leaks or use after fcloses.