fix(perf): explorer was creating new table for each new entry

augment performance on large folder by a factor of 10.
my /nix/store explorer goes from ~12sec to ~1.5sec.

lua/nvim-tree/explorer/explore.lua

@@ -15,13 +15,13 @@ end
 
 local function populate_children(handle, cwd, node, status)
   local node_ignored = node.git_status == "!!"
+  local nodes_by_path = utils.bool_record(node.nodes, "absolute_path")
   while true do
     local name, t = uv.fs_scandir_next(handle)
     if not name then
       break
     end
 
-    local nodes_by_path = utils.key_by(node.nodes, "absolute_path")
     local abs = utils.path_join { cwd, name }
     t = get_type_from(t, abs)
     if
@@ -42,6 +42,7 @@ local function populate_children(handle, cwd, node, status)
       end
       if child then
         table.insert(node.nodes, child)
+        nodes_by_path[child.absolute_path] = true
         common.update_git_status(child, node_ignored, status)
       end
     end