Update `segarray_test`

[ajpotts]

[ajpotts]

❌ Functions/methods with no direct unit tests

• from_return_msg (server-return JSON parsing)
• nbytes property
• to_ndarray / tolist (conversion functions aren’t explicitly tested, though some doctest coverage exists)
• OR / AND / XOR (grouped boolean ops)
• nunique
• aggregate (generic grouping)
• unique (per-subarray unique values)
• hash (segment hash)
• update_hdf
• to_parquet
• register / unregister / is_registered
• transfer

✅ Summary: The core segmentation, concatenation, selection, and setops APIs are well covered. The missing test coverage is mainly in:

• Server-facing / persistence (from_return_msg, update_hdf, to_parquet, register/unregister/is_registered, transfer)
• Secondary groupby aggregations (OR, AND, XOR, nunique, aggregate, unique)
• Utilities (nbytes, to_ndarray, tolist, hash)