fix: correctly propagate custom Protocols to http.Server

- Implemented \`applyDefaultServerConfig\` in \`Engine\` to apply \`serverProtocols\` to \`http.Server\`.
- Uncommented all calls to \`applyDefaultServerConfig\` in \`serve.go\`.
- Refactored \`SetProtocols\` and added internal \`setProtocols\` to ensure user-defined protocols are not overwritten by framework defaults in \`RunTLS\`.
- Added exhaustive tests in \`protocols_test.go\` to verify protocol inheritance and persistence.

protocols_test.go

@@ -0,0 +1,111 @@
+package touka
+
+import (
+	"crypto/tls"
+	"net/http"
+	"testing"
+)
+
+func TestApplyDefaultServerConfig(t *testing.T) {
+	engine := New()
+
+	// 1. 测试默认协议
+	srv1 := &http.Server{}
+	engine.applyDefaultServerConfig(srv1)
+
+	if srv1.Protocols == nil {
+		t.Fatal("srv1.Protocols should not be nil after applyDefaultServerConfig")
+	}
+
+	// 默认配置是 Http1: true, Http2: false, Http2_Cleartext: false
+	if !srv1.Protocols.HTTP1() {
+		t.Error("Expected HTTP/1 to be enabled by default")
+	}
+	if srv1.Protocols.HTTP2() {
+		t.Error("Expected HTTP/2 to be disabled by default")
+	}
+
+	// 2. 测试自定义协议
+	engine.SetProtocols(&ProtocolsConfig{
+		Http1:           true,
+		Http2:           true,
+		Http2_Cleartext: true,
+	})
+
+	srv2 := &http.Server{}
+	engine.applyDefaultServerConfig(srv2)
+
+	if srv2.Protocols == nil {
+		t.Fatal("srv2.Protocols should not be nil after applyDefaultServerConfig")
+	}
+
+	if !srv2.Protocols.HTTP1() {
+		t.Error("Expected HTTP/1 to be enabled after SetProtocols")
+	}
+	if !srv2.Protocols.HTTP2() {
+		t.Error("Expected HTTP/2 to be enabled after SetProtocols")
+	}
+	if !srv2.Protocols.UnencryptedHTTP2() {
+		t.Error("Expected Unencrypted HTTP/2 to be enabled after SetProtocols")
+	}
+
+	// 3. 再次更改协议并验证
+	engine.SetProtocols(&ProtocolsConfig{
+		Http1:           false,
+		Http2:           true,
+		Http2_Cleartext: false,
+	})
+
+	srv3 := &http.Server{}
+	engine.applyDefaultServerConfig(srv3)
+
+	if srv3.Protocols == nil {
+		t.Fatal("srv3.Protocols should not be nil")
+	}
+	if srv3.Protocols.HTTP1() {
+		t.Error("Expected HTTP/1 to be disabled")
+	}
+	if !srv3.Protocols.HTTP2() {
+		t.Error("Expected HTTP/2 to be enabled")
+	}
+}
+
+func TestRunTLSProtocolInheritance(t *testing.T) {
+	engine := New()
+
+	// 模拟 RunTLS 中的逻辑: 如果使用默认协议, 则启用 HTTP/2
+	if engine.useDefaultProtocols {
+		engine.setProtocols(&ProtocolsConfig{
+			Http1: true,
+			Http2: true,
+		})
+	}
+
+	srv := &http.Server{TLSConfig: &tls.Config{}}
+	engine.applyDefaultServerConfig(srv)
+
+	if !srv.Protocols.HTTP2() {
+		t.Error("RunTLS simulation: Expected HTTP/2 to be enabled for default config")
+	}
+
+	// 模拟用户设置了自定义协议后调用 RunTLS
+	engine = New()
+	engine.SetProtocols(&ProtocolsConfig{
+		Http1: true,
+		Http2: false, // 用户明确不想要 HTTP/2
+	})
+
+	if engine.useDefaultProtocols {
+		engine.setProtocols(&ProtocolsConfig{
+			Http1: true,
+			Http2: true,
+		})
+	}
+
+	srv2 := &http.Server{TLSConfig: &tls.Config{}}
+	engine.applyDefaultServerConfig(srv2)
+
+	if srv2.Protocols.HTTP2() {
+		t.Error("RunTLS simulation: Expected HTTP/2 to be DISABLED if user set custom protocols previously")
+	}
+}