Add support for optional namespace prefixes on JetStreamEventStore streams
to enable complete namespace isolation at the storage level:
- Add Namespace field to JetStreamConfig
- Add NewJetStreamEventStoreWithNamespace convenience constructor
- Prefix stream names with sanitized namespace when configured
- Add GetNamespace and GetStreamName accessor methods
- Add unit tests for namespace functionality
- Document namespace-scoped stores in CLAUDE.md
The namespace prefix is sanitized (spaces, dots, wildcards converted to
underscores) and prepended to the stream name, ensuring events from one
namespace cannot be read from another namespace's store while maintaining
full backward compatibility for non-namespaced stores.
Closes#19
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
