DEPR: rename 'unit' keyword in to_datetime etc

[jbrockmendel]

to_datetime, to_timedelta, Timestamp, and Timedelta have a unit keyword that causes confusion because the term 'unit' is overloaded. The keyword refers to how we interpret integer arguments, while the result's obj.unit attribute refers to the resolution of the result. Confusion e.g. #60371.

Update: also the meaning of the keyword in date_range matches the attribute but not the to_datetime meaning.

Let's deprecate the argument and rename it to something else. Opening bid: "numeric_unit"

[rhshadrach]

What if we made unit apply to non-numeric arguments? I.e. if a non-numeric argument is provided we convert to the user-specified unit? This would allow us to avoid code churn.

[jbrockmendel]

What if we made unit apply to non-numeric arguments? I.e. if a non-numeric argument is provided we convert to the user-specified unit? This would allow us to avoid code churn.

Do you mean "interpret 'unit' as specifying the desired output-unit in some cases but not atll"? i think im against more-overloading like that