REST Proxy: schema-to-subject validation can be bypassed with name_strategy_validation=true

When producing Avro messages through Karapace REST Proxy with `name_strategy_validation=true`, schema-to-subject validation can be bypassed in a real user flow.
If I first produce to topic A using a schema (so the proxy has already resolved that schema), then produce to topic B with the same schema, the second produce can succeed even though topic B has no corresponding subject in Schema Registry and should be rejected.
Expected behavior: with `name_strategy_validation=true`, producing to topic B should fail unless the schema is registered under topic B’s subject.
Actual behavior: after a prior successful produce on another topic, producing to topic B may still succeed, which looks like a cache-related validation gap.

### Example
Schema Registry ACL: the REST user can register subjects only for `topic.v1`.
The request body is the same in all three cases:
```json
{
"key_schema": "\"string\"",
"value_schema": "..."
"records": [...]
```

1. `POST http://localhost:8082/topics/topic.v2` -> Error
```json
{
"error_code": 40801,
"message": "Error when registering schema.format = AVRO, subject = topic.v2-value"
}
```

2. `POST http://localhost:8082/topics/topic.v1` -> Success
```json
{
"key_schema_id": 1,
"offsets": [
{
"offset": 5,
"partition": 0
}
],
"value_schema_id": 2
}
```
3. `POST http://localhost:8082/topics/topic.v2` -> Unexpected success (should have failed)
```json
{
"key_schema_id": 1,
"offsets": [
{
"offset": 3,
"partition": 0
}
],
"value_schema_id": 2
}
```
Also:
```
curl -u admin:pass localhost:8081/subjects
["topic.v1-key","topic.v1-value"]
```
So no new subjects were registered.