Address PR review feedback: replace dynamic await import() with static
top-level imports using vi.hoisted() for mock declarations, and remove
all `as any` type casts since the SDK constructor types already accept
the options we pass.
Each test mocks the AI SDK provider factory and asserts that all options
from the SDK client instance are forwarded. Compile-time exhaustiveness
guards ensure the tests break if the AI SDK provider types add new
options that need to be handled.
Jordan Ritter