(new): JSON HTML escaping control

- add Formatter.JSONEscapeHTML and SetJSONEscapeHTML to let JSON writers preserve HTML-sensitive characters when needed while keeping escaping enabled by default.
- switch JSON output to json.Encoder, preserve existing Print/Println newline semantics, and cover the new escaping behavior in tests.

writers.go

@@ -1,6 +1,7 @@
 package sneklog
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -145,21 +146,27 @@ func (w *LoggerJsonWriter) Print(level LogLevel, prefix string, traceback []*Met
 		Message:   s,
 		Traceback: traceback,
 	}
-	var data []byte
-	var err error
+
+	buf := bytes.NewBuffer(nil)
+	enc := json.NewEncoder(buf)
+	enc.SetEscapeHTML(f.JSONEscapeHTML)
 	if w.pretty {
-		data, err = json.MarshalIndent(m, "", "  ")
-	} else {
-		data, err = json.Marshal(m)
+		enc.SetIndent("", "  ")
 	}
+
+	err := enc.Encode(m)
 	if err != nil {
 		return err
 	}
-	if newline {
-		data = append(data, '\n')
+	data := buf.Bytes()
+	if !newline {
+		data = bytes.TrimSuffix(data, []byte("\n"))
 	}
-	_, err = w.Write(data)
-	return err
+	_, err = w.writer.Write(data)
+	if err != nil {
+		return err
+	}
+	return nil
 }
 
 // Close closes the owned writer, if any.