Import anthropic/openai/google-genai only when a provider is first used
instead of at module import. CLIENTS is now populated lazily via
default_client(), which preserves the patch.dict test seam. The
embedding client defers its SDK imports the same way and dispatches on
transport instead of isinstance.
Cuts idle RSS by ~60MiB per process with all three providers configured
but unused at startup; a process that only ever calls one provider also
never pays for the other two.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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