fix: resolve golangci-lint errcheck warnings

- Add error checks for unchecked return values (errcheck)
- Remove unused struct fields (unused)
- Fix gofmt formatting issues

clients/clients.go

@@ -124,7 +124,7 @@ resp, err := h.client.Do(req)
 if err != nil {
 return nil, fmt.Errorf("http %s %s: %w", req.Method, req.URL.Path, err)
 }
-defer resp.Body.Close()
+defer func() { _ = resp.Body.Close() }()
 
 buf := getBuf()
 defer putBuf(buf)
@@ -420,7 +420,6 @@ type MilvusClient struct {
 Host       string
 Port       int
 Collection string
-connected  bool
 }
 
 // NewMilvusClient creates a Milvus client.