Use `nvim_buf_get_text` instead of `nvim_buf_get_lines` to properly handle
column positions in visual selections. Add special handling for Visual Line
mode by adjusting start and end columns accordingly.

for more information, see https://pre-commit.ci

- Updated `get_selection` and `highlight_selection` functions to handle
  start and end columns for more precise selection highlighting.
- Modified `ask` function to maintain consistent indentation.
- Added `start_col` and `end_col` fields to selection object in
  `select.lua`.

for more information, see https://pre-commit.ci

Add an optional callback parameter to telescope.pick() function that gets
called after an action is selected. This allows for custom handling of
selected actions instead of the default ask behavior.

Change the trigger character for prompts from '/' to '!' to avoid conflicts with
Neovim's search functionality. This improves the user experience by preventing
accidental searches when using CopilotChat prompts.