Implement writing with categoricals

We can't currently write categoricals to DeltaLake.

import pandas as pd
import numpy as np
import dask.dataframe as dd
from dask_deltatable.write import to_deltalake

if __name__ == "__main__":
    df = pd.DataFrame({
        "i1": np.random.randint(1, 10000, size=100),
        "f1": np.random.random(100),
        "c1": pd.Series(np.random.choice(["Apple", "Banana", "Watermelon", "Mango"], size=100), dtype="category"),
    })
    ddf = dd.from_pandas(df, npartitions=10)
    to_deltalake("t4_data", ddf).compute()

This raises:

Traceback (most recent call last):
  File "/Users/jbennet/src/dask-deltatable/t4.py", line 14, in <module>
    to_deltalake("t4_data", ddf).compute()
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/base.py", line 310, in compute
    (result,) = compute(self, traverse=False, **kwargs)
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/base.py", line 595, in compute
    results = schedule(dsk, keys, **kwargs)
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/threaded.py", line 89, in get
    results = get_async(
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/local.py", line 511, in get_async
    raise_exception(exc, tb)
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/local.py", line 319, in reraise
    raise exc
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/local.py", line 224, in execute_task
    result = _execute_task(task, data)
  File "/Users/jbennet/mambaforge/envs/dask-deltatable/lib/python3.9/site-packages/dask/core.py", line 121, in _execute_task
    return func(*(_execute_task(a, cache) for a in args))
  File "/Users/jbennet/src/dask-deltatable/dask_deltatable/write.py", line 180, in _commit
    _write_new_deltalake(
Exception: Schema error: Invalid data type for Delta Lake: Dictionary(Int8, Utf8)

Pyarrow supports writing categories; delta-rs does not.

dask-contrib / dask-deltatable

Implement writing with categoricals #31