Add key management operations (Rename, Type, Dump/Restore)

[imperugo]

Summary

Add essential key management methods to `IRedisDatabase`.

Missing Methods

```csharp
Task KeyRenameAsync(string key, string newKey, When when = When.Always, CommandFlags flag = CommandFlags.None);
Task KeyTypeAsync(string key, CommandFlags flag = CommandFlags.None);
Task<byte[]?> KeyDumpAsync(string key, CommandFlags flag = CommandFlags.None);
Task KeyRestoreAsync(string key, byte[] value, TimeSpan? expiry = null, CommandFlags flag = CommandFlags.None);
```

Implementation

4 thin wrappers on SE.Redis `IDatabase` methods. ~15 lines total.