Rename "max rank" to "max dimensions" in capabilities()

[asmeurer]

See https://github.com/data-apis/array-api/pull/763#issuecomment-2138355341. "Rank" is an ambiguous term and "dimensions" is clearer. Although other names like "max ndims" would also be OK.

This is an unreleased API, and it's new in all implementations, so there should not be a concern with renaming it.