Fix oversubscription with CHPL_LOCALE_MODEL=gpu

[jhh67]

The PRs to add GPU support to co-locales (PRs https://github.com/chapel-lang/chapel/pull/25734 and https://github.com/chapel-lang/chapel/pull/25846) broke oversubscription such that no locales had any GPUs. This PR fixes that problem, and cleans up resource allocation with co-locales in general. Oversubscription is handled more cleanly, as is the "remainder" node that occurs when the number of locales is not evenly divisible by the number of nodes.

Signed-off-by: John H. Hartman [email protected]