[BUG] RPC client registration does not persist upstream status changes in selector handles

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/shenyu/issues) and found no similar issues.

### Apache ShenYu Component

shenyu-admin

### What happened

The Dubbo, gRPC, and Tars client registration services detect upstream status changes, but they do not apply those changes to the `existList` that is serialized back into the selector handle.

For example, `ShenyuClientRegisterGrpcServiceImpl.buildHandle(...)` does this:

```java
List existList = GsonUtils.getInstance().fromCurrentList(selectorDO.getHandle(), GrpcUpstream.class);
...
List diffStatusList = addList.stream().filter(upstream -> !upstream.isStatus()
|| existList.stream().anyMatch(e -> e.equals(upstream) && e.isStatus() != upstream.isStatus())).collect(Collectors.toList());
if (CollectionUtils.isNotEmpty(diffStatusList)) {
canAddList.addAll(diffStatusList);
}
...
return GsonUtils.getInstance().toJson(CollectionUtils.isEmpty(existList) ? canAddList : existList);
```

The same pattern exists in the Dubbo and Tars registration services.

The upstream `equals(...)` methods compare identity fields such as host/protocol/url/namespace, but they do not include `status`. Therefore a status-only change is detected in `diffStatusList`, but the matching object already in `existList` keeps its old status. Since the method serializes `existList` when it is not empty, the selector handle written back to DB still contains the stale status.

This affects status changes such as a single-node deleted/offline event where the new upstream is marked `status=false` before diffing.

### Expected behavior

When an existing upstream is re-registered with a different status, the matching item inside `existList` should be updated before the handle is serialized. The persisted selector handle should reflect the same status change that the registration flow detected.

### How to reproduce

1. Register a Dubbo, gRPC, or Tars upstream so the selector handle contains the upstream with `status=true`.
2. Send a registration event for the same upstream with `EventType.DELETED`, causing the newly built upstream to be marked `status=false`.
3. `diffStatusList` detects the changed status and adds it to `canAddList`.
4. Because `existList` is not updated, the method returns `GsonUtils.toJson(existList)` with the original `status=true` value.
5. The DB selector handle remains stale, so admin display/export/restart replay can use the old upstream status.

### Debug logs

_No response_

### Environment

Current `master` branch.

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

Start with ShenyuClientRegisterGrpcServiceImpl.buildHandle(...) and trace the corresponding Dubbo and Tars registration-service implementations, focusing on how existList is compared and serialized. Reproduce a status-only re-registration for an existing upstream, then verify that the persisted selector handle reflects the changed status for all three protocols.

Written by the indexing model from the issue text.