Confusion around Keyspace APIs

## Bug Report

### What did you do?

I am evaluating the Keyspace APIs that are supported by TiKV API v2 (https://github.com/tikv/client-rust). I am running TiUP locally. I created a non-default keyspace "foo" as follows:

```
curl -H 'Content-Type: application/json' \
-d '{ "name": "foo"}' \
-X POST \
127.0.0.1:19165/pd/api/v2/keyspaces
{
"id": 1,
"name": "foo",
"state": "ENABLED",
"created_at": 1712076752,
"state_changed_at": 1712076752
}%
```

Looking for the keyspaces:

```
curl 127.0.0.1:19165/pd/api/v2/keyspaces
{
"keyspaces": [
{
"id": 0,
"name": "DEFAULT",
"state": "ENABLED",
"created_at": 1712076651,
"state_changed_at": 1712076651
},
{
"id": 1,
"name": "foo",
"state": "ENABLED",
"created_at": 1712076752,
"state_changed_at": 1712076752
}
],
"
```

I am using the TiKV rust client and looks like all the operations are working against the "foo" keyspace.

Now, I decide to disable the "foo" keyspace as follow:

```
curl -H 'Content-Type: application/json' \
-d '{ "state": "DISABLED"}' \
-X PUT \
127.0.0.1:19165/pd/api/v2/keyspaces/foo/state
{
"id": 1,
"name": "foo",
"state": "DISABLED",
"created_at": 1712076752,
"state_changed_at": 1712077470
}%
```

The keyspace foo is disabled:

```
curl 127.0.0.1:19165/pd/api/v2/keyspaces
{
"keyspaces": [
{
"id": 0,
"name": "DEFAULT",
"state": "ENABLED",
"created_at": 1712076651,
"state_changed_at": 1712076651
},
{
"id": 1,
"name": "foo",
"state": "DISABLED",
"created_at": 1712076752,
"state_changed_at": 1712077470
}
],
"next_page_token": ""
}%
```

Now I send the same operations to the disabled Keyspace.

### What did you expect to see?
I expect all operations to fail for the disabled Keyspace. Both PD and Storage Node (tikv) should honor the disabled status of the keyspace and not return any results associated with keys prefixed with the keyspace identifier.

### What did you see instead?
All operations are returning keys and values from the disabled keyspace.

### What version of PD are you using (`pd-server -V`)?
Using Tiup /.tiup/components/playground/**v1.13.1**/tiup-playground --mode tikv-slim --pd.port 19165 --kv.config tikv.yaml