Facing problem when loading BERTopic Online Model

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Hi @MaartenGr ,

**I am facing the below issue when, I try to load an Online BERTopic model from my disk.

Issue --> 'In order to use `.partial_fit`, the cluster model should have a `.partial_fit` function.'

I tried to debug the code flow where I found that in BERTopic.load() we have a function call to _create_model_from_files() which loads the saved model.
The logic goes like this
```
empty_dimensionality_model = BaseDimensionalityReduction()
empty_cluster_model = BaseCluster()

# Fit BERTopic without actually performing any clustering
topic_model = BERTopic(
embedding_model=embedding_model,
umap_model=empty_dimensionality_model,
hdbscan_model=empty_cluster_model,
**params
)
```
Here, for Online Topic Models we use River.DBSTREAM as cluster model. But when we save the model using BERTopic.save() [in safetensors format] we are not storing the cluster model data.... Because of that, While loading back we face this issue..

Is there any quick fix for this issue??**

Start with BERTopic.load() and _create_model_from_files(), then compare them with BERTopic.save() using the safetensors format. Trace how the River.DBSTREAM cluster model is handled during saving and loading; done means an online model can be loaded and used with .partial_fit without the missing-method error.

Written by the indexing model from the issue text.