Fixed: #2034

feat(proxy): centralize proxy handling with `proxyutil` package and enhance test coverage

- Added `proxyutil` package to simplify proxy handling across the codebase.
- Refactored various components (`executor`, `cliproxy`, `auth`, etc.) to use `proxyutil` for consistent and reusable proxy logic.
- Introduced support for "direct" proxy mode to explicitly bypass all proxies.
- Updated tests to validate proxy behavior (e.g., `direct`, HTTP/HTTPS, and SOCKS5).
- Enhanced YAML configuration documentation for proxy options.

internal/runtime/executor/proxy_helpers_test.go

@@ -0,0 +1,30 @@
+package executor
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	cliproxyauth "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/auth"
+	sdkconfig "github.com/router-for-me/CLIProxyAPI/v6/sdk/config"
+)
+
+func TestNewProxyAwareHTTPClientDirectBypassesGlobalProxy(t *testing.T) {
+	t.Parallel()
+
+	client := newProxyAwareHTTPClient(
+		context.Background(),
+		&config.Config{SDKConfig: sdkconfig.SDKConfig{ProxyURL: "http://global-proxy.example.com:8080"}},
+		&cliproxyauth.Auth{ProxyURL: "direct"},
+		0,
+	)
+
+	transport, ok := client.Transport.(*http.Transport)
+	if !ok {
+		t.Fatalf("transport type = %T, want *http.Transport", client.Transport)
+	}
+	if transport.Proxy != nil {
+		t.Fatal("expected direct transport to disable proxy function")
+	}
+}