* mp: only count the offload cost of math once
This was previously bundling the combined weight storage and computation
cost
* ops: put all post async transfer compute on the main stream
Some models have massive weights that need either complex
dequantization or lora patching. Don't do these patchings on the offload
stream, instead do them on the main stream to syncrhonize the
potentially large vram spikes for these compute processes. This avoids
having to assume a worst case scenario of multiple offload streams
all spiking VRAM is parallel with whatever the main stream is doing.
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