`from_dataframe` gets a `cast_extension_array` argument

Is your feature request related to a problem?

To resolve the ongoing discussion around extension array casting, an option that has arisen would be to add a cast_extension_array argument (see https://github.com/pydata/xarray/issues/10301#issuecomment-2866569942 as well) to from_dataframe in order to give users "old" behavior (see #10301 for an exmaple where this might help).

Whether this is default true or false is up for debate probably but I think this is a great feature independent of the chaos that has arisen.

Describe the solution you'd like

from_dataframe gets a cast_extension_array argument

Describe alternatives you've considered

The alternative would basically be continuing to fix things as they arise and being totally permissive. But that is what is going to likely happen anyway (i.e., you can set on a Dataset with an extension array type anyway given this feature, no issue).

Additional context

cc @dcherian @keewis

Start at the from_dataframe entry point and read the linked #10301 discussion to understand the extension-array casting behavior and unresolved default. Done means the new argument is supported with an agreed default and tests demonstrate both the existing and alternative casting behavior.