## Description
When opening a terminal with position='current', the terminal buffer
wasn't being set in the current window, causing the original buffer
content to remain visible with terminal styling applied.
This fix adds a call to vim.api.nvim_win_set_buf() to properly set the
terminal buffer when using position='current'. Also updates type
annotations to include the 'current' position option and adds tests to
prevent regression.
Credit to the solution to by @Baricus in issue #2148.
## Related Issue(s)
Fixes#2148
Co-authored-by: Baricus <31926270+Baricus@users.noreply.github.com>
