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

ggml/src/ggml-webgpu/ggml-webgpu.cpp

@@ -1245,7 +1245,7 @@ static webgpu_encoded_op ggml_webgpu_gated_delta_net(webgpu_context & ctx,
     const uint32_t h        = (uint32_t) src2->ne[1];
     const uint32_t n_tokens = (uint32_t) src2->ne[2];
     const uint32_t n_seqs   = (uint32_t) src2->ne[3];
-    const uint32_t K        = (uint32_t) src5->ne[1];
+    const uint32_t K        = (uint32_t) ggml_get_op_params_i32(dst, 0);
     const float    scale    = 1.0f / sqrtf((float) s_v);
     uint32_t       scale_u32;
     memcpy(&scale_u32, &scale, sizeof(scale_u32));