style: discard unused params in default hook impls

lua/flatten/init.lua

@@ -145,6 +145,7 @@ Flatten.callbacks = Callbacks
 ---@param argv string[]
 ---@return boolean
 function Callbacks.should_block(argv)
+  local _ = argv
   return false
 end
 
@@ -192,19 +193,19 @@ end
 ---Called before a nested session is opened.
 ---@param opts Flatten.PreOpenContext
 function Callbacks.pre_open(opts)
-  return
+  local _ = opts
 end
 
 ---Called after a nested session is opened.
 ---@param opts Flatten.PostOpenContext
 function Callbacks.post_open(opts)
-  return
+  local _ = opts
 end
 
 ---Called when a nested session is done waiting for the host.
 ---@param opts Flatten.BlockEndContext
 function Callbacks.block_end(opts)
-  return
+  local _ = opts
 end
 
 ---Executed when there are no files to open, to determine whether