Add missing dunder methods to SizeDict

[hmellor]

Some libraries that use Transformers (i.e. vLLM) use | on the size config.

This PR adds __or__ and __ror__ so that the following works:

$ {"longest_edge": 20} | SizeDict(height=10, width=20)
{'longest_edge': 20, 'height': 10, 'width': 20}
$ SizeDict(height=10, width=20) | {"longest_edge": 20}
SizeDict(height=10, width=20, longest_edge=20, shortest_edge=None, max_height=None, max_width=None)
$ SizeDict(height=10, width=20) | SizeDict(longest_edge=20)
SizeDict(height=10, width=20, longest_edge=20, shortest_edge=None, max_height=None, max_width=None)

[zucchini-nlp]

Looks reasonable, I think we want to keep treating SizeDict as normal dict. Approving to unblock vlllm

[HuggingFaceDocBuilderDev]

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