graph: store the MTP conv snapshots of every recurrent model in one set_rows (#31660)
* graph: store the conv state of every rollback arch in one set_rows
The rollback slots of the causal conv history were written with one
copy per slot in qwen4exp, glm5-next, kimi-k3, bailingmoe3, lfm and
mamba2, while delta_net already wrote them with a single set_rows.
build_conv_state_store now does this for all of them: one copy without
rollback, otherwise one set_rows of the overlapping windows into the
min(n, n_rs_seq + 1) slots a rollback can read.
The slot order {n_rs_seq, ..., 0} is computed once per graph and each
conv layer takes a view of its tail. Its size does not depend on the
ubatch, so the reserved graph covers every ubatch shape, and the graph
input that held it is gone.
A model that is not causal never rolls back, so the context clamps
n_rs_seq to 0 for it, like for an arch without rollback support.
* nits: compute the conv slot order in the graph and keep the n_head name of bailingmoe3
* graph: build the conv slot order in each conv layer
The slot order {K-1, ..., 0} of the conv state store was one tensor
shared by every conv layer of the graph, built on the device of the
first one, so each layer on another device copied the view of its
tail. Each conv layer now builds its own order next to its set_rows,
and llm_graph_input_rs no longer holds it.