PERF: DTA/TDA _simple_new disallow i8 values
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

thanks, assume the perf benefit is for microbenchmarks FTR I think this fixes https://github.com/HypothesisWorks/hypothesis/issues/2894