rebase: bump golang.org/x/net from 0.37.0 to 0.38.0 in /e2e

Bumps [golang.org/x/net](https://github.com/golang/net) from 0.37.0 to 0.38.0.
- [Commits](https://github.com/golang/net/compare/v0.37.0...v0.38.0)

---
updated-dependencies:
- dependency-name: golang.org/x/net
  dependency-version: 0.38.0
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

e2e/vendor/github.com/prometheus/client_golang/prometheus/collectorfunc.go

@@ -0,0 +1,30 @@
+// Copyright 2025 The Prometheus Authors
+// Licensed 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.
+
+package prometheus
+
+// CollectorFunc is a convenient way to implement a Prometheus Collector
+// without interface boilerplate.
+// This implementation is based on DescribeByCollect method.
+// familiarize yourself to it before using.
+type CollectorFunc func(chan<- Metric)
+
+// Collect calls the defined CollectorFunc function with the provided Metrics channel
+func (f CollectorFunc) Collect(ch chan<- Metric) {
+	f(ch)
+}
+
+// Describe sends the descriptor information using DescribeByCollect
+func (f CollectorFunc) Describe(ch chan<- *Desc) {
+	DescribeByCollect(f, ch)
+}

e2e/vendor/github.com/prometheus/client_golang/prometheus/promhttp/http.go

@@ -41,11 +41,11 @@ import (
 	"sync"
 	"time"
 
-	"github.com/klauspost/compress/zstd"
 	"github.com/prometheus/common/expfmt"
 
 	"github.com/prometheus/client_golang/internal/github.com/golang/gddo/httputil"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp/internal"
 )
 
 const (
@@ -65,7 +65,13 @@ const (
 	Zstd     Compression = "zstd"
 )
 
-var defaultCompressionFormats = []Compression{Identity, Gzip, Zstd}
+func defaultCompressionFormats() []Compression {
+	if internal.NewZstdWriter != nil {
+		return []Compression{Identity, Gzip, Zstd}
+	} else {
+		return []Compression{Identity, Gzip}
+	}
+}
 
 var gzipPool = sync.Pool{
 	New: func() interface{} {
@@ -138,7 +144,7 @@ func HandlerForTransactional(reg prometheus.TransactionalGatherer, opts HandlerO
 	// Select compression formats to offer based on default or user choice.
 	var compressions []string
 	if !opts.DisableCompression {
-		offers := defaultCompressionFormats
+		offers := defaultCompressionFormats()
 		if len(opts.OfferedCompressions) > 0 {
 			offers = opts.OfferedCompressions
 		}
@@ -466,14 +472,12 @@ func negotiateEncodingWriter(r *http.Request, rw io.Writer, compressions []strin
 
 	switch selected {
 	case "zstd":
-		// TODO(mrueg): Replace klauspost/compress with stdlib implementation once https://github.com/golang/go/issues/62513 is implemented.
-		z, err := zstd.NewWriter(rw, zstd.WithEncoderLevel(zstd.SpeedFastest))
-		if err != nil {
-			return nil, "", func() {}, err
+		if internal.NewZstdWriter == nil {
+			// The content encoding was not implemented yet.
+			return nil, "", func() {}, fmt.Errorf("content compression format not recognized: %s. Valid formats are: %s", selected, defaultCompressionFormats())
 		}
-
-		z.Reset(rw)
-		return z, selected, func() { _ = z.Close() }, nil
+		writer, closeWriter, err := internal.NewZstdWriter(rw)
+		return writer, selected, closeWriter, err
 	case "gzip":
 		gz := gzipPool.Get().(*gzip.Writer)
 		gz.Reset(rw)
@@ -483,6 +487,6 @@ func negotiateEncodingWriter(r *http.Request, rw io.Writer, compressions []strin
 		return rw, selected, func() {}, nil
 	default:
 		// The content encoding was not implemented yet.
-		return nil, "", func() {}, fmt.Errorf("content compression format not recognized: %s. Valid formats are: %s", selected, defaultCompressionFormats)
+		return nil, "", func() {}, fmt.Errorf("content compression format not recognized: %s. Valid formats are: %s", selected, defaultCompressionFormats())
 	}
 }

e2e/vendor/github.com/prometheus/client_golang/prometheus/promhttp/internal/compression.go

@@ -0,0 +1,21 @@
+// Copyright 2025 The Prometheus Authors
+// Licensed 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.
+
+package internal
+
+import (
+	"io"
+)
+
+// NewZstdWriter enables zstd write support if non-nil.
+var NewZstdWriter func(rw io.Writer) (_ io.Writer, closeWriter func(), _ error)