Add an option to set pixel threshold in bytes

[hombit]

Feature request

It would be very useful to threshold pixels by in-memory-size instead of number of rows. This would provide more homogeneous pixels sizes when using nested types such as lists, strings and bytes. It is useful for datasets like ZTF DRs or ZTF/LSST alerts.

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• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
• I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
• If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.