Multiple services support the notion of the model requesting multiple tool calls in a single roundtrip, as well as the ability to disable that so that at most one tool call can be requested at a time. We should consider promoting that to be a strongly-typed property on ChatOptions, rather than weakly-typed in a provider-specific manner.

(We should also do another tour through all the major providers, looking for commonalities that might lead to other settings getting promoted because they're now ubiquitous.)