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.

iprawsock.go

@@ -1,4 +1,4 @@
-// TINYGO: The following is copied and modified from Go 1.21.4 official implementation.
+// TINYGO: The following is copied and modified from Go 1.26.2 official implementation.
 
 // Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -8,6 +8,7 @@ package net
 
 import (
 	"errors"
+	"net/netip"
 	"syscall"
 )
 
@@ -26,8 +27,18 @@ import (
 // BUG(mikio): On JS and Plan 9, methods and functions related
 // to IPConn are not implemented.
 
-// BUG(mikio): On Windows, the File method of IPConn is not
-// implemented.
+// BUG: On Windows, raw IP sockets are restricted by the operating system.
+// Sending TCP data, sending UDP data with invalid source addresses,
+// and calling bind with TCP protocol don't work.
+//
+// See Winsock reference for details.
+
+func ipAddrFromAddr(addr netip.Addr) *IPAddr {
+	return &IPAddr{
+		IP:   addr.AsSlice(),
+		Zone: addr.Zone(),
+	}
+}
 
 // IPAddr represents the address of an IP end point.
 type IPAddr struct {
@@ -80,14 +91,14 @@ func ResolveIPAddr(network, address string) (*IPAddr, error) {
 	return nil, errors.New("ResolveIPAddr not implemented")
 }
 
-// IPConn is the implementation of the Conn and PacketConn interfaces
+// IPConn is the implementation of the [Conn] and [PacketConn] interfaces
 // for IP network connections.
 type IPConn struct {
 	conn
 }
 
 // SyscallConn returns a raw network connection.
-// This implements the syscall.Conn interface.
+// This implements the [syscall.Conn] interface.
 func (c *IPConn) SyscallConn() (syscall.RawConn, error) {
 	return nil, errors.New("SyscallConn not implemented")
 }
@@ -114,7 +125,7 @@ func (c *IPConn) WriteToIP(b []byte, addr *IPAddr) (int, error) {
 	return 0, errors.New("WriteToIP not implemented")
 }
 
-// WriteTo implements the PacketConn WriteTo method.
+// WriteTo implements the [PacketConn] WriteTo method.
 func (c *IPConn) WriteTo(b []byte, addr Addr) (int, error) {
 	return 0, errors.New("WriteTo not implemented")
 }