Add back convenience imports

having util hang around everywhere is germane to my development
experience. I use util.log a lot, heh.

Also the previous commit breaks the tests by altering a fixture
file, which should never be altered.

lua/treewalker/init.lua

@@ -1,4 +1,5 @@
 local nodes = require('treewalker.nodes')
+local util = require('treewalker.util')
 local ops = require('treewalker.ops')
 local lines = require('treewalker.lines')
 local strategies = require('treewalker.strategies')
@@ -16,7 +17,9 @@ Treewalker.opts = {
 
 ---@param opts Opts | nil
 function Treewalker.setup(opts)
-  Treewalker.opts = vim.tbl_deep_extend('force', Treewalker.opts, opts or {})
+  if opts then
+    Treewalker.opts = vim.tbl_deep_extend('force', Treewalker.opts, opts)
+  end
 end
 
 ---@return nil

lua/treewalker/strategies.lua

@@ -1,5 +1,6 @@
 local lines = require('treewalker.lines')
 local nodes = require('treewalker.nodes')
+local util  = require('treewalker.util')
 
 ---@alias Dir "up" | "down"
 

tests/fixtures/lua.lua

@@ -1,3 +1,5 @@
+local util = require('treewalker.util')
+
 local M = {}
 
 local NON_TARGET_NODE_MATCHERS = {
@@ -26,7 +28,7 @@ local function is_jump_target(node)
 end
 
 local function is_descendant_jump_target(node)
-  return vim.list_contains(TARGET_DESCENDANT_TYPES, node:type())
+  return util.contains(TARGET_DESCENDANT_TYPES, node:type())
 end
 
 ---Do the nodes have the same starting point