[FEATURE]: Support non-factory LanguageModelV2 class exports in dynamic provider loader #16793

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Describe the enhancement you want to request

The dynamic provider loader only recognizes npm packages that export a create* factory. Some packages (e.g. @augmentcode/auggie-sdk) export a LanguageModelV2 class directly — no factory wrapper. These fail to load.

Proposal: add a fallback that duck-types LanguageModelV2 classes (doGenerate + doStream on prototype) and wraps them in a minimal provider object. The create* path stays preferred; class detection is the fallback.

Constructor convention: Every standard Vercel AI SDK provider uses (modelId, config) as the constructor signature:

The two outliers (OpenRouter, ai-gateway-provider) both export create* factories, so the class fallback would never trigger for them. Function.length can be used as a runtime guard to reject constructors that don't take exactly 2 args.

This unblocks Augment Code support (#10216) and future-proofs the loader for any SDK that ships a raw LanguageModelV2 without a factory.