[THIS-1078] 🐝 Allow no client (#1580)

# Description

In CDF notebooks, we do not need a Client as NeatSession creates it for
you. Thus, we should set the default to `None`. This saves code lines
creating a new session .
<img width="660" height="321" alt="image"
src="https://github.com/user-attachments/assets/c33a3dec-d273-4bba-908e-53b48a1224ff"
/>


## Bump

- [x] Patch
- [ ] Skip

## Changelog
### Improved

- When creating a `NeatSession` in a CDF notebook, you do not have to
pass a `CogniteClient`.

Author: doctrino

cognite/neat/_session/_session.py

@@ -28,7 +28,9 @@ class NeatSession:
     """A session is an interface for neat operations."""
 
     def __init__(
-        self, client: CogniteClient | ClientConfig | None, config: PredefinedProfile | NeatConfig = "legacy-additive"
+        self,
+        client: CogniteClient | ClientConfig | None = None,
+        config: PredefinedProfile | NeatConfig = "legacy-additive",
     ) -> None:
         """Initialize a Neat session.