logging: implement lazy sprinting (#8898)

shout out to @joeabbey for the inspiration. This makes the lazy
functions internal by default to prevent potential misuse by external
callers.

Should backport cleanly into 0.36 and I'll handle a messy merge into 0.35

rpc/jsonrpc/server/http_server.go

@@ -58,7 +58,7 @@ func DefaultConfig() *Config {
 // Serve creates a http.Server and calls Serve with the given listener. It
 // wraps handler to recover panics and limit the request body size.
 func Serve(ctx context.Context, listener net.Listener, handler http.Handler, logger log.Logger, config *Config) error {
-	logger.Info(fmt.Sprintf("Starting RPC HTTP server on %s", listener.Addr()))
+	logger.Info("Starting RPC HTTP server on", "addr", listener.Addr())
 	h := recoverAndLogHandler(MaxBytesHandler(handler, config.MaxBodyBytes), logger)
 	s := &http.Server{
 		Handler:        h,