update_metadata accepts string, but then breaks node

[nmaytan]

If you call update_metadata from a client, it will accept a simple string argument (as it is serializable), but then causes server 500's when doing anything with that node.

The metadata should be type checked before being accepted as an update.

client:

In [5]: l['C']
Out[5]: <ArrayClient shape=(10, 10) chunks=((10,), (10,)) dtype=float64>

In [6]: l['C'].update_metadata(metadata="test")

In [7]: l['C']
Scheduled retry in 0.54 seconds due to HTTPStatusError("Server error '500 Internal Server Error' for url 'http://localhost:8000/api/v1/metadata/C'\nFor more information, server admin can search server logs for correlation ID 576705178793e1d6.") (attempt 1)

server:

pydantic_core._pydantic_core.ValidationError: 1 validation error for NodeAttributes
metadata
  Input should be a valid dictionary [type=dict_type, input_value='test', input_type=str]
    For further information visit https://errors.pydantic.dev/2.11/v/dict_type