重构: User 默认实现移到 req/userx，消除 req 对 contracts 的循环依赖

GetAnonymous/GetSystemUser 原来在 contracts/base 里实现，req 自己的测试
又要用它们构造测试用户，形成 req（测试）依赖 contracts、contracts（正式
代码）依赖 req 的循环——两边 go.mod 只能靠指向本地兄弟目录的 replace 绕过，
没法各自独立解析成真实版本号。

跟 resx 之于 req.Resource 一个思路：接口留在 req 包，默认实现挪到子包
req/userx，req 主包保持不引入实现细节所需的依赖（这里是 samber/lo）。
req 自己的测试文件改用 req/userx，不用触碰 contracts 了；contracts/base
里的 GetAnonymous/GetSystemUser 改成指向 req/userx 的函数别名，保持
兼容不用改调用方。

resx/res_normalize_test.go

@@ -4,11 +4,11 @@ import (
 	"strings"
 	"testing"
 
-	"git.fsdpf.net/go/contracts/base"
 	"git.fsdpf.net/go/db"
 	"git.fsdpf.net/go/db/engine"
 	"git.fsdpf.net/go/req"
 	"git.fsdpf.net/go/req/resx"
+	"git.fsdpf.net/go/req/userx"
 	"github.com/DATA-DOG/go-sqlmock"
 	"github.com/samber/do/v2"
 	"github.com/stretchr/testify/suite"
@@ -56,7 +56,7 @@ func (t *normalizeTest) TestStripsSystemFields() {
 		resx.NewResField("name", "", resx.FieldWithName("姓名"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{
 			"id":           999,
 			"name":         "张三",
@@ -83,7 +83,7 @@ func (t *normalizeTest) TestDropsUndeclaredFields() {
 		resx.NewResField("name", "", resx.FieldWithName("姓名"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "李四", "hacker_field": "evil"},
 	).Executor().ToSQL()
 
@@ -99,7 +99,7 @@ func (t *normalizeTest) TestExpressionValuePassesThroughEvenIfUndeclared() {
 		resx.NewResField("name", "", resx.FieldWithName("姓名"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "王五", "login_at": db.L("NOW()")},
 	).Executor().ToSQL()
 
@@ -114,7 +114,7 @@ func (t *normalizeTest) TestJSONFieldNilUsesFieldDefault() {
 		resx.NewResField("fields", "", resx.FieldWithName("字段"), resx.FieldWithDefault("[]"), resx.FieldWithDataType(req.ResJson)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "A", "fields": nil},
 	).Executor().ToSQL()
 
@@ -131,7 +131,7 @@ func (t *normalizeTest) TestJSONFieldDefaultFilledWhenOmitted() {
 		resx.NewResField("fields", "", resx.FieldWithName("字段"), resx.FieldWithDefault("{}"), resx.FieldWithDataType(req.ResJson)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "B"},
 	).Executor().ToSQL()
 
@@ -146,7 +146,7 @@ func (t *normalizeTest) TestNonJSONFieldDefaultNotAutoFilled() {
 		resx.NewResField("name", "", resx.FieldWithName("姓名"), resx.FieldWithDefault("匿名"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{},
 	).Executor().ToSQL()
 
@@ -161,7 +161,7 @@ func (t *normalizeTest) TestOwnedUserDefaultsToCurrentUserWhenUndeclared() {
 		resx.NewResField("name", "", resx.FieldWithName("姓名"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "C", "owned_user": "someone-else-uuid"},
 	).Executor().ToSQL()
 
@@ -178,7 +178,7 @@ func (t *normalizeTest) TestOwnedUserPreservedWhenDeclaredAsField() {
 		resx.NewResField("owned_user", "", resx.FieldWithName("拥有者"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "D", "owned_user": "someone-else-uuid"},
 	).Executor().ToSQL()
 
@@ -193,7 +193,7 @@ func (t *normalizeTest) TestCreatedUserAlwaysForcedToCurrentUser() {
 		resx.NewResField("created_user", "", resx.FieldWithName("创建者"), resx.FieldWithDataType(req.ResString)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Insert().Rows(
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Insert().Rows(
 		db.Record{"name": "E", "created_user": "someone-else-uuid"},
 	).Executor().ToSQL()
 
@@ -212,7 +212,7 @@ func (t *normalizeTest) TestNormalizeSaveValue_Update() {
 		resx.NewResField("fields", "", resx.FieldWithName("字段"), resx.FieldWithDefault("{}"), resx.FieldWithDataType(req.ResJson)),
 	)
 
-	sql, _, _ := res.GetDBTable(base.GetAnonymous()).Update().
+	sql, _, _ := res.GetDBTable(userx.GetAnonymous()).Update().
 		Set(db.Record{
 			"id":         1,
 			"name":       "F",