feature: center cursor in lines picker

[kocv59]

Did you check the docs?

• I have read all the snacks.nvim docs

Is your feature request related to a problem? Please describe.

I have a large scrolloff to center the cursor. The lines picker uses the bottom of the screen but the cursor is still centered in the whole screen not the part of the screen excluding the picker.

Describe the solution you'd like

Pickers should center the text so there's context for the line.

Describe alternatives you've considered

Use the regular search not the lines picker.

Additional context

No response