Merge local and remote GPU shapes index, preferring Object Storage overrides

[mrDzurb]

Description:

This PR enhances the load_gpu_shapes_index function to merge GPU-shape definitions from two sources—an OCI Object Storage bucket and a local JSON file, so that any shapes defined remotely override their local counterparts, while still falling back cleanly if the remote load fails.

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What Changed

1. Separate remote vs. local loads

   • We now load remote_data and local_data into two distinct dictionaries.
   • If the CONDA_BUCKET_NS environment variable is set, we attempt to read from Object Storage.

2. Merge logic

   • After loading both sources, we merge the two on the "shapes". Any entry present in remote_data["shapes"] overrides the same key in local_data, while preserving local entries not present remotely.

3. Return the merged index

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[VipulMascarenhas]

looks good. I was thinking if local shapes should override the remote ones and not the other way round. But probably makes sense to keep default as remote to avoid bad shape combinations that might lead to failures.