Upgrade net package from Go 1.21.4 to Go 1.26.2

Backport upstream Go standard library changes to TinyGo's net package.

Unmodified files (18) replaced directly from Go 1.26.2 source.
Modified files (22) merged via 3-way diff, preserving all TinyGo
netdev adaptations, TINYGO markers, and embedded-device constraints.

Notable upstream changes included:
- net/http: cookie handling improvements, fs enhancements,
  reverse proxy updates, chunked encoding fixes
- net/http: ServeMux routing and pattern matching updates
- net: IP parsing and MAC address handling improvements
- Various doc link syntax modernization (e.g. [Dial], [Buffers])

TinyGo-only files (netdev.go, tlssock.go) unchanged.
All TINYGO comment markers preserved.

http/clone.go

@@ -1,6 +1,4 @@
-// TINYGO: The following is copied from Go 1.21.4 official implementation.
-
-// Copyright 2019 The Go Authors. All rights reserved.
+// TINYGO: The following is copied from Go 1.26.2 official implementation.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -10,8 +8,18 @@ import (
 	"mime/multipart"
 	"net/textproto"
 	"net/url"
+	_ "unsafe" // for linkname
 )
 
+// cloneURLValues should be an internal detail,
+// but widely used packages access it using linkname.
+// Notable members of the hall of shame include:
+//   - github.com/searKing/golang
+//
+// Do not remove or change the type signature.
+// See go.dev/issue/67401.
+//
+//go:linkname cloneURLValues
 func cloneURLValues(v url.Values) url.Values {
 	if v == nil {
 		return nil
@@ -21,6 +29,15 @@ func cloneURLValues(v url.Values) url.Values {
 	return url.Values(Header(v).Clone())
 }
 
+// cloneURL should be an internal detail,
+// but widely used packages access it using linkname.
+// Notable members of the hall of shame include:
+//   - github.com/searKing/golang
+//
+// Do not remove or change the type signature.
+// See go.dev/issue/67401.
+//
+//go:linkname cloneURL
 func cloneURL(u *url.URL) *url.URL {
 	if u == nil {
 		return nil
@@ -34,6 +51,15 @@ func cloneURL(u *url.URL) *url.URL {
 	return u2
 }
 
+// cloneMultipartForm should be an internal detail,
+// but widely used packages access it using linkname.
+// Notable members of the hall of shame include:
+//   - github.com/searKing/golang
+//
+// Do not remove or change the type signature.
+// See go.dev/issue/67401.
+//
+//go:linkname cloneMultipartForm
 func cloneMultipartForm(f *multipart.Form) *multipart.Form {
 	if f == nil {
 		return nil
@@ -42,7 +68,7 @@ func cloneMultipartForm(f *multipart.Form) *multipart.Form {
 		Value: (map[string][]string)(Header(f.Value).Clone()),
 	}
 	if f.File != nil {
-		m := make(map[string][]*multipart.FileHeader)
+		m := make(map[string][]*multipart.FileHeader, len(f.File))
 		for k, vv := range f.File {
 			vv2 := make([]*multipart.FileHeader, len(vv))
 			for i, v := range vv {
@@ -55,6 +81,15 @@ func cloneMultipartForm(f *multipart.Form) *multipart.Form {
 	return f2
 }
 
+// cloneMultipartFileHeader should be an internal detail,
+// but widely used packages access it using linkname.
+// Notable members of the hall of shame include:
+//   - github.com/searKing/golang
+//
+// Do not remove or change the type signature.
+// See go.dev/issue/67401.
+//
+//go:linkname cloneMultipartFileHeader
 func cloneMultipartFileHeader(fh *multipart.FileHeader) *multipart.FileHeader {
 	if fh == nil {
 		return nil
@@ -67,6 +102,16 @@ func cloneMultipartFileHeader(fh *multipart.FileHeader) *multipart.FileHeader {
 
 // cloneOrMakeHeader invokes Header.Clone but if the
 // result is nil, it'll instead make and return a non-nil Header.
+//
+// cloneOrMakeHeader should be an internal detail,
+// but widely used packages access it using linkname.
+// Notable members of the hall of shame include:
+//   - github.com/searKing/golang
+//
+// Do not remove or change the type signature.
+// See go.dev/issue/67401.
+//
+//go:linkname cloneOrMakeHeader
 func cloneOrMakeHeader(hdr Header) Header {
 	clone := hdr.Clone()
 	if clone == nil {