Expose inferBatch, trainEx, moveWeightsEx, evalLoss, and getLayerStats
from the WASM binary into the JavaScript layer:
- inferBatch: batch inference for heatmap sampling
- trainEx: replaces train() with per-iteration loss history capture
- moveWeightsEx: native output pin mask support (removes save/restore hack)
- evalLoss: compute loss without updating weights
- getLayerStats: per-layer weight statistics (meanAbs, maxAbs, dead/sat fracs)
Worker also upgraded to trainEx, returning full lossHistory in payload.
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