docs(typing): Fix inaccurate selection_interval signature

[dangotbanned]

Resolves #3653 (comment)

Primarily addresses mark: Mark, which should be mark: BrushConfig.

As @mattijn noted, interactions-parameter-composition would produce this waring:

Argument of type "BrushConfig" cannot be assigned to parameter "mark" of type "Optional[Mark]" in function "selection_interval"
  Type "BrushConfig" is not assignable to type "Optional[Mark]"
    "BrushConfig" is not assignable to "Mark"
    "BrushConfig" is not assignable to "UndefinedType"

I traced this back to:

• https://github.com/vega/altair/blame/374a07f0aa7605b1d5ef96f9bfd32d73723f3ca9/altair/vegalite/v5/api.py#L523
  • Introduction of the annotation
• https://github.com/vega/altair/blame/374a07f0aa7605b1d5ef96f9bfd32d73723f3ca9/altair/vegalite/v5/api.py#L574
  • The docstring it appears to have been based on

---

It was also asked was whether this can be set within a theme.
I found that indeed this would be possible (BrushConfigKwds).

I spotted some others which seemed useful to include (MergedStreamKwds, DerivedStreamKwds).

Note

I think the strange docs these have is due to being defined recursively.

---

Finally, this PR updates/corrects the typing embedded within the docstring