1. FPTemporary usage 2. hypot update

1. Remove `FPTemporary` usage in `std.complex`.
2. Remove `FPTemporary` usage in `std.numeric`.
3. Change `hypot` to `template`.
4. Clean up imports in `std.complex`.
5. Clean up imports in `std.numeric`.
6. Change `isfinite` to `isFinite` in `std.numeric`.