KeyValue.keys() with filters fetches all keys from server causing performance issues

[TarasLykhenko]

Observed behavior

When using the keys() method with filters on a KeyValue store containing a large number of keys (thousands or more), the method fetches all keys from the server and filters them client-side using substring matching. This creates significant performance problems and server load.

Expected behavior

The KeyValue keys() method should perform server-side filtering to minimize network traffic and server load, similar to how the Go client implements this functionality.

Server and client version

• NATS Server: 2.12.1
• nats-py: current main branch
• Python: 3.11+

Host environment

No response

Steps to reproduce

No response

[arturoriter]

I had to stop using the filter and I did the following:

                keys = []
                watcher = await kv.watch(keys=key, ignore_deletes=True, meta_only=True)
                async for entry in watcher:
                    if not entry:
                        break
                    keys.append(entry.key)
                await watcher.stop()

Now it's filtering on the server side