feat: enable diagnostics (#891)

lua/avante/range.lua

@@ -5,7 +5,7 @@ local Range = {}
 Range.__index = Range
 
 ---@class avante.RangeSelection: table<string, integer>
----@field line number
+---@field lnum number
 ---@field col number
 
 ---Create a selection range
@@ -18,4 +18,17 @@ function Range:new(start, finish)
   return instance
 end
 
+---Check if the line and column are within the range
+---@param lnum number Line number
+---@param col number Column number
+---@return boolean
+function Range:contains(lnum, col)
+  local start = self.start
+  local finish = self.finish
+  if lnum < start.lnum or lnum > finish.lnum then return false end
+  if lnum == start.lnum and col < start.col then return false end
+  if lnum == finish.lnum and col > finish.col then return false end
+  return true
+end
+
 return Range