hparams : refactor hparams.n_layer (#24060)

* hparams : refactor hparams.n_layer

* cont : remove `n_layer_kv()`, use n_layer_all instead

* cont : type consistency

* pi : update SYSTEM.md

* models : fix Step3.5 MTP

* cont : remove duplicate switch cases

* cont : explicitly set `false` to extra layers for `is_swa` and `is_recr`

* cont : fix nextn layer count handling

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

---------

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

src/llama-model-loader.cpp

@@ -1050,10 +1050,10 @@ struct ggml_tensor * llama_model_loader::create_tensor(
         if (it == ctx_map.end()) {
             // one ggml context per buffer type
             int max_n_tensors = n_tensors;
-            max_n_tensors += 1;                 // duplicated output tensor
-            max_n_tensors += hparams.n_layer*2; // duplicated rope freq tensors
+            max_n_tensors += 1;                   // duplicated output tensor
+            max_n_tensors += hparams.n_layer()*2; // duplicated rope freq tensors
             if (files.empty()) {
-                max_n_tensors += hparams.n_layer*256; // this should be well above what any model actually uses
+                max_n_tensors += hparams.n_layer()*256; // this should be well above what any model actually uses
             }
             const size_t ctx_size = ggml_tensor_overhead()*max_n_tensors;