fix: detect modified user limits and refresh limiter state

[besnow]

Motivation

• 现有用户同步只分为 deleted / added，通过 UUID+SpeedLimit 判断变化会漏掉 DeviceLimit 或 Id 的变更，导致节点端 limiter 状态不同步。
• 目标是最小改动修复：以 UUID 为主键，增加 modified 分类并在 limiter 层刷新对应用户的限速 / 设备限制。

Description

• 将 compareUserList 从返回 (deleted, added) 升级为 (deleted, added, modified)，仅以 Uuid 为键，若 SpeedLimit、DeviceLimit 或 Id 发生变化则归类为 modified（修改文件：node/user.go）。
• 在用户同步流程中接收三类结果：added 仍走 AddUsers，deleted 仍走 DelUsers，modified 不再触发 add/del；当任一非空时调用 c.limiter.UpdateUser(c.tag, added, deleted, modified) 并在日志中输出三类计数（修改文件：node/task.go）。
• 将 limiter.UpdateUser 签名改为 UpdateUser(tag string, added, deleted, modified []panel.UserInfo)，保留原有 add/delete 逻辑并新增 modified 处理：就地更新 UserLimitInfo 的 UID/SpeedLimit/DeviceLimit、刷新 UUIDtoUID，并在 SpeedLimit 变更时删除对应的 SpeedLimiter bucket 以迫使后续建立新桶；若记录不存在则按 added 逻辑补建（修改文件：limiter/limiter.go）。
• 添加 compareUserList 单元测试覆盖无变化/新增/删除/SpeedLimit 变更/DeviceLimit 变更/相同 UUID 且限制不变不列为 modified（新增文件：node/user_test.go）。

Testing

• 已运行格式化：gofmt -w node/user.go node/task.go limiter/limiter.go node/user_test.go，格式化成功。
• 已运行单元和包测试：go test ./...，测试通过（包含新增的 compareUserList 测试）。
• 已运行构建：go build ./...，构建成功。

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Codex Task

[chatgpt-codex-connector]

💡 Codex Review

V2bX/node/task.go

Lines 194 to 200 in 6c17ea8

	if len(added) > 0 {
	// have added users
	_, err = c.server.AddUsers(&vCore.AddUsersParams{
	Tag: c.tag,
	NodeInfo: c.info,
	Users: added,
	})

Refresh core UID mapping for modified users

When a user's Id changes but Uuid stays the same, this path marks the user as modified and skips c.server.AddUsers, so the core's UID mapping is never updated. In core/xray/user.go, uidMap is only rewritten inside AddUsers, and GetUserTrafficSlice reads that map to populate reported UID; as a result, traffic continues to be attributed to the old UID after an ID-only change. This commit introduces that mismatch because modified users now update limiter state but not the core user map.

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[besnow]

SpeedLimit / DeviceLimit 发生变化时归类为 modified。
Id-only change 不归类为 modified，因为 V2Board 中 UUID -> user ID 是稳定映射。