Fix actions receiving nil instance

Action callbacks were being called with 'nil' instead of an instance. This commit fixes the action buffer type and passes 'instance' to the action callback.

src/apply.luau

@@ -14,7 +14,7 @@ type Node<T> = graph.Node<T>
 local event_buffer: { [string]: () -> () } = {}
 
 -- buffer of priority -> callback to run after events are connected
-local action_buffers = {} :: { { () -> () } }
+local action_buffers = {} :: { { (Instance) -> () } }
 setmetatable(action_buffers :: any, {
     __index = function(_, i: number)
         action_buffers[i] = {}
@@ -131,7 +131,7 @@ local function apply<T>(instance: T & Instance, properties: { [unknown]: unknown
     -- run buffered actions respecting their priorities
     for _, buffer in next, action_buffers do
         for _, callback in next, buffer do
-            callback()
+            callback(instance)
         end
     end