Remove padding and multiple D2D copies for MTP (#24086)

* Make ggml_gated_delta_net take only the initial recurrent state (D, 1, n_seqs) and passes the snapshot count K as an op parameter instead of inferring it from state->ne[1].

Remove the padding hack and copy all emitted snapshots into the recurrent cache with a single strided ggml_cpy

* Make GDN changes in all backends. Address review comments.

* Fix CI build errors

src/models/models.h

@@ -46,7 +46,7 @@ struct llm_build_delta_net_base : public llm_graph_context {
                 ggml_tensor * s,
                 int           il);
 
-    // use the ggml_gated_delta_net fused operator (K=1; state has shape (D, 1, n_seqs))
+    // use the ggml_gated_delta_net fused operator (K=1; state has shape [S_v, S_v, H_v, n_seqs])
     std::pair<ggml_tensor *, ggml_tensor *> build_delta_net_fused(
                 ggml_tensor * q,
                 ggml_tensor * k,