String columns come back as `Utf8` even when cardinality is tiny — is that expected?

Hey!

We've been using both `adbc_snowflake` and `databricks-adbc` to pull data, and we noticed that string columns always come back as plain `Utf8`, no matter how repetitive the values are. Even when a 1M-row column has only 10 distinct values, we get a flat `Utf8` array rather than `Dictionary`.

A few questions:

1. **Is this the intended behavior?** We weren't sure whether the warehouse ships strings as dictionary-encoded on the wire and the driver flattens them, or whether they always come in flat from the source.
2. **Is there an option we're missing?** Something to either preserve dictionary encoding (if it exists upstream), or otherwise get `Dictionary` back from the driver?
3. **If there isn't, would you be open to adding one?** Something like a cardinality threshold — columns where the distinct-to-row-count ratio is below some limit get cast to `Dictionary` before reaching the consumer.

It matters to us because we serialize the data to Arrow IPC and send it over a network. Dictionary-encoded strings are a few times smaller on the wire and the decoder on the other end has a fast path for that type. Today we walk each `RecordBatch` ourselves and cast qualifying `Utf8` columns to dictionaries — it works, but it feels like the kind of thing that should live in the driver, especially since every consumer doing IPC over a network probably wants the same thing.

Happy to share more detail if useful. Thanks!