perf: remove unnecessary allocations in hot-path processors

Remove wasteful Clone() calls and defer allocations in docker metadata,
kubernetes metadata, timestamp, and publisher/processing processors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: strawgate

changelog/fragments/1774755443-remove-unnecessary-allocations.yaml

@@ -0,0 +1,5 @@
+kind: enhancement
+summary: Remove unnecessary allocations in hot-path processors (docker metadata, kubernetes metadata, dissect, timestamp)
+component: libbeat
+pr:
+  - https://github.com/elastic/beats/pull/49761

libbeat/beat/event_test.go

@@ -129,7 +129,7 @@ func TestEvent(t *testing.T) {
 			event := &Event{}
 			require.NotPanics(t, func() {
 				s := event.String()
-				require.JSONEq(t, `{"@metadata":{},"@timestamp":"0001-01-01T00:00:00Z"}`, s)
+				require.Equal(t, `{"@metadata":{},"@timestamp":"0001-01-01T00:00:00Z"}`, s)
 			})
 		})
 	})

libbeat/processors/add_docker_metadata/add_docker_metadata.go

@@ -218,7 +218,7 @@ func (d *addDockerMetadata) Run(event *beat.Event) (*beat.Event, error) {
 		_, _ = meta.Put("container.id", container.ID)
 		_, _ = meta.Put("container.image.name", container.Image)
 		_, _ = meta.Put("container.name", container.Name)
-		event.Fields.DeepUpdate(meta.Clone())
+		event.Fields.DeepUpdate(meta)
 	} else {
 		d.log.Debugf("Container not found: cid=%s", cid)
 	}

libbeat/processors/add_docker_metadata/add_docker_metadata_benchmark_test.go

@@ -0,0 +1,71 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build (linux || darwin || windows) && !integration
+
+package add_docker_metadata
+
+import (
+	"testing"
+
+	"github.com/elastic/beats/v7/libbeat/beat"
+	"github.com/elastic/elastic-agent-autodiscover/docker"
+	conf "github.com/elastic/elastic-agent-libs/config"
+	"github.com/elastic/elastic-agent-libs/logp/logptest"
+	"github.com/elastic/elastic-agent-libs/mapstr"
+)
+
+func BenchmarkAddDockerMetadata(b *testing.B) {
+	cfg, err := conf.NewConfigFrom(map[string]interface{}{
+		"match_fields": []string{"container.id"},
+	})
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	p, err := buildDockerMetadataProcessor(logptest.NewTestingLogger(b, ""), cfg, MockWatcherFactory(
+		map[string]*docker.Container{
+			"abc123": {
+				ID:    "abc123def456",
+				Image: "myrepo/myimage:latest",
+				Name:  "my-container",
+				Labels: map[string]string{
+					"app":     "myapp",
+					"version": "v1.2.3",
+					"env":     "production",
+				},
+			},
+		}, nil))
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		event := &beat.Event{
+			Fields: mapstr.M{
+				"container": mapstr.M{"id": "abc123"},
+				"message":   "test log line",
+			},
+		}
+		_, err := p.Run(event)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}