Implement a duckdb backend

[ahuang11]

As duckdb popularity rises, I think it makes sense to add support for it, even if it's a thin wrapper

import pandas as pd
import duckdb

pd.DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": ["a", "b", "c"]}).to_parquet("example.parquet")

connection = duckdb.connect()
relation = connection.from_parquet("example.parquet").to_view("example")

relation = connection.execute("SELECT * FROM example")
relation.fetchdf().hvplot()  <- # simplify this to relation.hvplot()

[ahuang11]

Seems to work for a simple case :O

import hvplot.duckdb

import pandas as pd
import duckdb

df = pd.DataFrame({
    'x': [1, 2, 3],
    'y': [4, 5, 6]
})

df.to_parquet('test.parquet')

connection = duckdb.connect(database=':memory:', read_only=False)
connection.from_parquet("test.parquet").hvplot(
    x='x', y='y', kind='scatter'
)