llama : refactor kv cache guard (#12695)

* llama : refactor kv cache guard

ggml-ci

* cont : fix comment [no ci]

* llama : fix kv_cache restore logic

ggml-ci

* context : simplify kv cache updates

ggml-ci

* cont : better name [no ci]

* llama : fix llama_decode return code when could not find KV slot

ggml-ci

* context : change log err -> warn [no ci]

* kv-cache : add comment + warning

examples/parallel/parallel.cpp

@@ -106,6 +106,8 @@ int main(int argc, char ** argv) {
 
     common_params params;
 
+    params.n_predict = 128;
+
     if (!common_params_parse(argc, argv, params, LLAMA_EXAMPLE_PARALLEL)) {
         return 1;
     }