fix: stop window vars from throwing tantrums

Turns out nvim_win_get_var was a drama queen, throwing exceptions
whenever it couldn't find its precious variable - like a toddler having
a meltdown when they can't find their favorite toy.

Switched to vim.w, the more chill cousin who just returns nil and goes
about their day when something's missing. Now our code won't have an
existential crisis just because a directory hasn't changed.

No more exception-al behavior, just peaceful, quiet coding.

Author: liskin

lua/CopilotChat/init.lua

@@ -1331,7 +1331,7 @@ function M.setup(config)
     group = augroup,
     callback = function()
       if vim.v.event and vim.v.event.cwd then
-        vim.api.nvim_win_set_var(0, 'cchat_cwd', vim.v.event.cwd)
+        vim.w.cchat_cwd = vim.v.event.cwd
       end
     end,
   })

lua/CopilotChat/utils.lua

@@ -176,7 +176,7 @@ function M.win_cwd(winnr)
     return '.'
   end
 
-  local dir = vim.api.nvim_win_get_var(winnr, 'cchat_cwd')
+  local dir = vim.w[winnr].cchat_cwd
   if not dir or dir == '' then
     return '.'
   end