[pallas:fuser] Do not scalar prefetch inside nested calls in `push_block_spec` #41852

[pallas:fuser] Do not scalar prefetch inside nested calls in push_block_spec

Scalar prefetch values must come from fusion consts, but a nested call receives
all of its inputs as arguments. pull_block_spec already accounts for this,
while push_block_spec failed an assertion on nested ops with dynamic indices,
e.g. dynamic_update_slice, even when the push rule did not need them.