Incorrect handling of FEED subtable.

[JSKenyon]

Describe the bug
The FEED subtable may not be regular. QuartiCal assumes that it is.

To Reproduce
Attempt to access the FEED subtable on a zarr backed MS.

Expected behavior
QuartiCal should successfully read the FEED subtable.

Version
main

[JSKenyon]

This is partially fixed for the pressing case in #351 but will still affect the older parallactic angle code. I will fix this in a subsequent release.