fix: ensure help window width is an int

Problem:

The help window causes an error when calling `vim.api.nvim_open_win`
because the width being passed is not an integer.

Neovim's `vim.api.nvim_open_win` function requires that the width and
height be specified in whole integers.

The width is being calculated through a division operation causing it to
potentially be a number that is not an int.

Solution:

Floor the calculation of the help window width so the width is always
rounded down to the nearest integer and can thus be used with
`vim.api.nvim_open_win`.

lua/rest-nvim/result/help.lua

@@ -62,7 +62,7 @@ function help.open()
   end
 
   -- Help window sizing and positioning
-  local width = vim.api.nvim_win_get_width(winnr) / 2
+  local width = math.floor(vim.api.nvim_win_get_width(winnr) / 2)
   local height = 8
 
   local col = vim.api.nvim_win_get_width(winnr) - width - 4