Close#15119 when this is merged
# Description
> Note: my locale is +1
**Before the changes 🔴**

See the issue for more detailed description of the problem.
**After the changes 🟢**

# User-Facing Changes
The ``into datetime`` command will now work with formatting and time
zones or offset together
# Tests + Formatting
Fmt + clippy OK
**Note about the tests I added**: those tests don't really test my
changes, as they were already passing before my changes. Nevertheless I
thought I could push them
# After Submitting
I don't think anything is necessary
# Description
Removes the old `nu-cmd-dataframe` crate in favor of the polars plugin.
As such, this PR also removes the `dataframe` feature, related CI, and
full releases of nushell.