speculative : fix n_outputs_max and remove draft-simple auto-enable (#23988)

* speculative : add common_speculative_n_max helper function

Extract the speculative max-draft-size logic from server_n_outputs_max
into a reusable common_speculative_n_max() function in common/speculative.

Assisted-by: llama.cpp:local pi

* cont : draft context always has n_parallel outputs

* llama : log n_outputs_max

* speculative : remove draft-simple auto-enable

* ci : enable server tests on PRs

common/arg.cpp

@@ -1041,11 +1041,9 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
     // we define here to make sure it's included in llama-gen-docs
     if (ex == LLAMA_EXAMPLE_COMPLETION) {
         params.use_jinja = false;   // disable jinja by default
-
     } else if (ex == LLAMA_EXAMPLE_MTMD) {
         params.use_jinja = false;   // disable jinja by default
         params.sampling.temp = 0.2; // lower temp by default for better quality
-
     } else if (ex == LLAMA_EXAMPLE_SERVER) {
         params.n_parallel = -1;     // auto by default
     }
@@ -1066,7 +1064,6 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
         sampler_type_names.pop_back(); // remove last semicolon
     }
 
-
     /**
      * filter options by example
      * rules:
@@ -1080,7 +1077,6 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
         }
     };
 
-
     add_opt(common_arg(
         {"-h", "--help", "--usage"},
         "print usage and exit",