Support datetime column in for rasterize selector

[hoxbro]

The following will show hover information as numbers and not as datetimes.

import holoviews as hv
import numpy as np
import pandas as pd
import datashader as ds
from holoviews.operation.datashader import rasterize

hv.extension("bokeh")

n = 10000
df = pd.DataFrame(
    {
        "x": np.random.uniform(-180, 180, n),
        "y": np.random.uniform(-90, 90, n),
        "Timestamp": pd.date_range(start="2023-01-01", periods=n, freq="D"),
        "Value": np.random.rand(n) * 100,
    }
)

rasterize(hv.Points(df), aggregator=ds.count(), selector=ds.first("Value")).opts(tools=["hover"])

First discovered in holoviz/hvplot#1206