Have explicit "Inheritance Model" paragraph

[rouault]

spatial lacks a clear paragraph like the one of proj in https://github.com/zarr-conventions/geo-proj?tab=readme-ov-file#inheritance-model . I assume they are the same reading"When defined at the group level: Properties apply to direct child arrays that don't define their own spatial: properties", but a dedicated paragraph would be more explicit

CC @emmanuelmathot

[wietzesuijker]

Working on GeoZarr support across a few libraries. The spec is missing a paragraph explaining that group-level spatial: attributes apply to child arrays. The proj: convention has this explicitly — a matching paragraph in spatial: could make the two feel like a coherent pair. Suggestion:

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Inheritance Model

The spatial: convention follows the same inheritance model as proj::

1. Group-level definition (recommended): When spatial: is defined at the group level, it applies to all arrays that are direct children of that group. It does not apply to groups or arrays deeper in the hierarchy.
2. Array-level override: An array can override the group's spatial: properties with its own definitions.