refactor: move converter from hrp internal to pkg

hrp/pkg/convert/from_json.go

@@ -0,0 +1,27 @@
+package convert
+
+import (
+	"github.com/pkg/errors"
+
+	"github.com/httprunner/httprunner/v4/hrp"
+	"github.com/httprunner/httprunner/v4/hrp/internal/builtin"
+)
+
+func LoadJSONCase(path string) (*hrp.TCase, error) {
+	// load json case file
+	caseJSON := new(hrp.TCase)
+	err := builtin.LoadFile(path, caseJSON)
+	if err != nil {
+		return nil, errors.Wrap(err, "load json file failed")
+	}
+
+	if caseJSON.TestSteps == nil {
+		return nil, errors.New("invalid json case file, missing teststeps")
+	}
+
+	err = caseJSON.MakeCompat()
+	if err != nil {
+		return nil, err
+	}
+	return caseJSON, nil
+}