append method
Append new key/value rows for each head (each arg shape (T, headDim)).
Implementation
void append(List<Tensor2D> kNew, List<Tensor2D> vNew) {
if (kNew.length != nHeads || vNew.length != nHeads) {
throw ArgumentError('KV append: head count mismatch');
}
for (var h = 0; h < nHeads; h++) {
kHeads[h] = _concatRows(kHeads[h], kNew[h]);
vHeads[h] = _concatRows(vHeads[h], vNew[h]);
}
}