EventStore(max_events_per_stream=0) retains every event ID #5534

`EventStore` documents `max_events_per_stream` as the maximum number of events retained per stream, but accepts zero without validation. When trimming the stream index, Python evaluates `event_ids[-0:]` as `event_ids[0:]`, which keeps the full list instead of removing all entries.

With `EventStore(max_events_per_stream=0, ttl=None)`, a local reproduction stored 20 events and retained all 20 event IDs. A control configured with a limit of five retained five. The default cap of 100 is unaffected.

Could the constructor reject non-positive values, or define and implement explicit zero-cap behavior? The current behavior silently permits unbounded per-stream index growth for a configuration that appears to set the maximum to zero.

### Example Code

```Python

```

### Version Information

```Text
- FastMCP main: `5baeacfe20eca735cb949564b4915f93a622b916`
- Python: 3.12.15
- OS: macOS 15.0.1 arm64
```