Extract root-most widget to resolve (various) `.ui` import cycles
when the type is declared on `Struct`s..
Deats,
- flip to `from ._widget import GodWidget`.
- move `Feed` + `Flume` imports to TYPE_CHECKING in `._chart`
- drop unused `trio` import from `._chart`
- fix docstring typo: "datums```" -> "`datums``"
- change `print()` to `log.warning()` for global step msg
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code