chore: modernize CI and update Go toolchain

- Bump Go from 1.19 to 1.26 and update all dependencies
- Rewrite CI workflow with matrix strategy (Linux, macOS, Windows)
- Update GitHub Actions to current versions (checkout@v4, setup-go@v5)
- Update CodeQL actions from v1 to v3
- Fix cross-platform bug in mock/path.go (path.Join -> filepath.Join)
- Clean up dependabot config (weekly schedule, remove stale ignore)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/golang.org/x/net/proxy/per_host.go

@@ -7,6 +7,7 @@ package proxy
 import (
 	"context"
 	"net"
+	"net/netip"
 	"strings"
 )
 
@@ -57,7 +58,8 @@ func (p *PerHost) DialContext(ctx context.Context, network, addr string) (c net.
 }
 
 func (p *PerHost) dialerForRequest(host string) Dialer {
-	if ip := net.ParseIP(host); ip != nil {
+	if nip, err := netip.ParseAddr(host); err == nil {
+		ip := net.IP(nip.AsSlice())
 		for _, net := range p.bypassNetworks {
 			if net.Contains(ip) {
 				return p.bypass
@@ -108,8 +110,8 @@ func (p *PerHost) AddFromString(s string) {
 			}
 			continue
 		}
-		if ip := net.ParseIP(host); ip != nil {
-			p.AddIP(ip)
+		if nip, err := netip.ParseAddr(host); err == nil {
+			p.AddIP(net.IP(nip.AsSlice()))
 			continue
 		}
 		if strings.HasPrefix(host, "*.") {
@@ -137,9 +139,7 @@ func (p *PerHost) AddNetwork(net *net.IPNet) {
 // AddZone specifies a DNS suffix that will use the bypass proxy. A zone of
 // "example.com" matches "example.com" and all of its subdomains.
 func (p *PerHost) AddZone(zone string) {
-	if strings.HasSuffix(zone, ".") {
-		zone = zone[:len(zone)-1]
-	}
+	zone = strings.TrimSuffix(zone, ".")
 	if !strings.HasPrefix(zone, ".") {
 		zone = "." + zone
 	}
@@ -148,8 +148,6 @@ func (p *PerHost) AddZone(zone string) {
 
 // AddHost specifies a host name that will use the bypass proxy.
 func (p *PerHost) AddHost(host string) {
-	if strings.HasSuffix(host, ".") {
-		host = host[:len(host)-1]
-	}
+	host = strings.TrimSuffix(host, ".")
 	p.bypassHosts = append(p.bypassHosts, host)
 }