Refine debug logging for llm

This wires up logging in llama.cpp to always go to stderr, and also
turns up logging if OLLAMA_DEBUG is set.

llm/dyn_ext_server.go

@@ -136,6 +136,12 @@ func newDynExtServer(library, model string, adapters, projectors []string, opts
 
 	sparams.n_threads = C.uint(opts.NumThread)
 
+	if debug := os.Getenv("OLLAMA_DEBUG"); debug != "" {
+		sparams.verbose_logging = C.bool(true)
+	} else {
+		sparams.verbose_logging = C.bool(false)
+	}
+
 	slog.Info("Initializing llama server")
 	initResp := newExtServerResp(128)
 	defer freeExtServerResp(initResp)