Python SDK: expose client disconnect and shutdown lifecycle methods

### Description

The Rust `Client` trait exposes both `disconnect()` and `shutdown()`, while the Python `IggyClient` currently exposes only `connect()`.

`disconnect()` closes the current connection while allowing the client to connect again. `shutdown()` releases the underlying client resources and is terminal for binary transports.

This covers B7 and B8 of the Python SDK parity work tracked in #3893.

```rust
async fn disconnect(&self) -> Result<(), IggyError>;
async fn shutdown(&self) -> Result<(), IggyError>;
```

### Affected area / component

Python SDK

### Proposed solution

- Add asynchronous `disconnect()` and `shutdown()` methods to the `#[pymethods]` block in `foreign/python/src/client.rs`.
- Delegate directly to the corresponding Rust `IggyClient` methods and map failures through the existing `to_runtime_error` helper.
- Regenerate `foreign/python/apache_iggy.pyi`, with both methods returning `Awaitable[None]`.
- Extend `foreign/python/tests/test_connectivity.py` to verify:
- `disconnect()` is idempotent.
- Requests fail while disconnected.
- A disconnected client can connect and authenticate again.
- `shutdown()` is idempotent.
- Requests after shutdown fail with the underlying client-shutdown error.
- Document transport-specific behavior, including the no-op lifecycle used by HTTP.

No new wrapper types are needed.

### Alternatives considered

Expose only `disconnect()`. This would leave Python without the terminal cleanup operation provided by the Rust client.

### Contribution

- [ ] I'm willing to submit a pull request to implement this feature

### Good first issue

- [x] I think this could be a good first issue for a new contributor

Start in foreign/python/src/client.rs and inspect the existing #[pymethods] block and to_runtime_error helper, then compare the Rust Client trait methods. Update the generated foreign/python/apache_iggy.pyi and extend foreign/python/tests/test_connectivity.py for idempotence, reconnecting, disconnected requests, and shutdown failures. Done means the tests cover both lifecycle methods and the transport-specific behavior is documented.

Written by the indexing model from the issue text.