TYP: enforce tighter inputs on SingleBlockManager
there is currently only one place where we pass a list of indexes instead of a single index, so just fixed that and were good to go.
lgtm. rebase and @jorisvandenbossche has some comments, ping on green. @jorisvandenbossche i think ive addressed your comments, can you confirm? Yes, thanks.

One more thing, though. For `Block`, we actually deprecated `fastpath` first instead of directly removing (only the passing of the keyword, I mean, not any functionality, https://github.com/pandas-dev/pandas/pull/19265). I assume SingleBlockManager will be used less in practice, but it's also not much work to still accept fastpath and raise a warning for it for now. > deprecated `fastpath` first instead of directly removing

Sure Thanks!