A spilled hybrid got `-ot blk\.\d+\.ffn_.*\.weight=CPU`, which moves every
block's FFN — full-attention blocks included — regardless of how many bytes
actually had to leave the GPU. The GGUF reader now records FFN weight bytes
per block, and spill_overrides picks the fewest recurrent (n_head_kv==0)
blocks whose FFNs cover the decision's spill_bytes, emitting them as an
explicit `blk\.(i|j|...)\.ffn_.*\.weight=CPU` selector. Unknown sizes fall
back to every recurrent block, never a full-attention one.
Based on #120778 by @kvnloo (recurrent-index selector).
Covers the placement half of #113329; the overhead/logits calibration
(RUNTIME_OVERHEAD_BYTES, ub_logits_bytes) is untouched pending measured data.
Refs #113329
d619b67ec2