`list(filter(None, map(func, ...)))` is typed as `list[Unknown]` if `func`'s return type doesn't include `None`

**Describe the bug**

`list(filter(None, map(func, ...)))` is typed as `list[Unknown]` if `func`'s return type doesn't include `None`.

**Code or Screenshots**

Code sample in [pyright playground](https://pyright-play.net/?code=CYUwZgBGD20BQH0BcECWA7ALgSggWgD40skAoCCiAJxEwFcr0IBGU00SGaBaKhdaOhCIUGHPiJiIAHwgA5QSDKVqtBk1akwqADaYQfLhAC8UXfqpwFQgDQQAtgEMADnC52A2swC62bFvMDBC4ePgEhEzM9AytFOydXEN5%2BOIgvX39SGgA3EEcdBEwAT2dhbWjDWH8cvILi0rdAyu5k8JBMmvzCkuEdVABnTEaK4KrqkFyu%2Bt6BofKLUZawxT82TrqeuD7B4YtY2wcXN1hPHz8-CgBiCG3MDwBVdABrAQB3dG8sidruhtvdmLWEDxI5JZYHdLnXAQa63DxibxAA)

```python
def foo(_: int) -> int:
return 1

def foo_or_none(_: int) -> int | None:
return 1

filter_foo = filter(None, map(foo, [1]))
filter_foo_or_none = filter(None, map(foo_or_none, [1]))

reveal_type(filter_foo)
reveal_type(filter_foo_or_none)

reveal_type(list(filter_foo))
reveal_type(list(filter_foo_or_none))

reveal_type(list(filter(None, map(foo, [1])))) # list[Unknown]
reveal_type(list(filter(None, map(foo_or_none, [1])))) # list[int]
```

Start with the linked pyright playground and compare the four reveal_type results for filter/map with and without None in the callback return type. Trace the relevant type inference behavior, then confirm that the non-Optional callback case produces the intended list element type without changing the existing Optional case.

Written by the indexing model from the issue text.