fix for building docs on Windows
- [x] closes #60149

I was having two issues with building the docs on Windows.

1. Building a single page with `--single` was very slow because it was reading in lots of files.  So there is a fix in `conf.py` that changes any backslashes to `/` in the paths.  Probably a better fix is to not be using `os.join` and use `pathlib`, but that's a larger change.
2. For #60149, there are 2 issues with building `enhancingperf.rst`:
  - As mentioned in https://github.com/pandas-dev/pandas/issues/60149#issuecomment-2600578029 , having double quotes in the ipython strings messes up Windows, so changing them to single quotes makes it work
  - The cython functions expect `int64` dtypes, but the defaults coming from `numpy` when building the DF are `int32`, so the `astype(int)` calls fix that


Thanks @Dr-Irv 