We would like to learn about your use case. For example, if this feature is needed to adopt Narwhals in an open source project, could you please enter the link to it below?

use case for this came up in this PR of tubular azukds/tubular#366.

Please describe the purpose of the new feature or describe the problem to solve.

We want to select all datetime columns and currently have to define all of these:

TIME_UNITS = ["us", "ns", "ms"]
TIME_ZONES = zoneinfo.available_timezones().union({None})

DATETIME_VARIANTS = [
nw.Datetime(time_unit=time_unit, time_zone=time_zone)
for time_unit in TIME_UNITS
for time_zone in TIME_ZONES
]

datetime_columns = list(
X.select(ncs.by_dtype(*DATETIME_VARIANTS)).columns,)

Suggest a solution if possible.

I expect similar logic could be turned into an ncs.datetime selector function similar to current categorical/numeric.

If you have tried alternatives, please describe them below.

No response

Additional information that may help us understand your needs.

No response