ENH: infer freq in timedelta_range
xref #36582, #35897, #36595, #32377, #31195

there may be cases where a frequency should not be inferred by timedelta_range due to rounding issues

e.g. `pd.timedelta_range('0s','1s', periods=31)`

The docs https://pandas.pydata.org/pandas-docs/dev/reference/api/pandas.timedelta_range.html begin 'Return a fixed frequency TimedeltaIndex...' so having None (no inferred frequency) maybe not desirable.

cc @jbrockmendel @jreback @phofl 