✨ Implement full support for nested fields in Meta and Entry marshalling

This commit completes the implementation of nested field support.
- :
    -  now correctly handles  and  by recursively flattening them into  format.
    - Introduced  for recursive map marshalling.
    - Refactored  for cleaner buffer writing.
- : Added comprehensive test cases for nested JSON, nested maps, double-nested maps, and nested keys within JSON to ensure correct marshalling and unmarshalling.
- : Updated tests to reflect the new nil handling and removed redundant JSON object test.

This allows for more flexible and structured data representation within log entries.

models/meta.go

@@ -2,6 +2,7 @@ package models
 
 import (
 	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"regexp"
@@ -18,16 +19,63 @@ func (m Meta) MarshalText() ([]byte, error) {
 	if regexp.MustCompile(`\s`).MatchString(m.Key) {
 		return []byte{}, fmt.Errorf("whitespace is not allowed in key: %s", m.Key)
 	}
+
 	buff := &bytes.Buffer{}
+
+	if jv, ok := m.Value.(map[string]any); ok {
+		err := marshalMap(m.Key, jv, buff)
+		return buff.Bytes(), err
+	}
+
+	if jj, ok := m.Value.(json.RawMessage); ok {
+		mp := map[string]any{}
+		err := json.Unmarshal(jj, &mp)
+		if err == nil {
+			err := marshalMap(m.Key, mp, buff)
+			return buff.Bytes(), err
+		}
+	}
+
+	if err := m.marshalToBuff(buff); err != nil {
+		return nil, err
+	}
+
+	return buff.Bytes(), nil
+}
+
+func marshalMap(pre string, mp map[string]any, buff *bytes.Buffer) error {
+	var idx uint
+	for k, v := range mp {
+		if idx > 0 {
+			buff.WriteRune('\n')
+		}
+		idx++
+		if subM, ok := v.(map[string]any); ok {
+			if err := marshalMap(pre+":"+k, subM, buff); err != nil {
+				return err
+			}
+		} else {
+			mSub := Meta{pre + ":" + k, v}
+			if err := mSub.marshalToBuff(buff); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (m Meta) marshalToBuff(buff *bytes.Buffer) error {
 	buff.WriteRune('@')
 	buff.WriteString(m.Key)
 	buff.WriteRune(' ')
 	n, err := tools.WriteValue(buff, m.Value)
-	if n == 0 || err != nil {
-		return []byte{}, err
+	if err != nil {
+		return err
 	}
-
-	return buff.Bytes(), nil
+	if n == 0 {
+		return ErrorParsing
+	}
+	return nil
 }
 
 func (m *Meta) UnmarshalText(in []byte) error {