fix(plugin): CloseIdleConnections silent no-op when tokenTransport wraps HTTP transport

tokenTransport now delegates CloseIdleConnections to the underlying
*http.Transport so http.Client.CloseIdleConnections() works through
the wrapper. Three plugin Close() methods updated to unwrap via
HTTPClientTransport before calling CloseIdleConnections.

RoundTrip now short-circuits when caller already set Authorization,
avoiding an unnecessary req.Clone allocation on the pass-through path.

config/parsing/sd/parse.go

@@ -28,6 +28,7 @@ func ParseSD(cfg *config.SDConfig) sd.SD {
 	case "http":
 		return sd_plugin.NewHTTPPlugin(
 			cfg.Name, cfg.Plugin.Addr,
+			plugin.TokenOption(cfg.Plugin.Token),
 			plugin.TLSConfigOption(tlsCfg),
 			plugin.TimeoutOption(cfg.Plugin.Timeout),
 		)