fix: prevent infinite loop when typing out anonymous function

`fn ->)` is a common intermediate state when writing anonymous function
and when the editor closes the bracket, putting the cursor inside. This
was causing an infinite loop, because it did not consume a token. This
is because of special handling of some tokens.

Same happened to :eof.

Author: katafrakt

lib/spitfire.ex

@@ -2180,7 +2180,7 @@ defmodule Spitfire do
 
                     {ast, parser} =
                       cond do
-                        current_token(parser) == :-> and peek_token(parser) == :end ->
+                        current_token(parser) == :-> and peek_token(parser) in [:")", :end, :eof] ->
                           parser = next_token(parser)
                           {ast, parser}
 

test/spitfire_test.exs

@@ -2348,6 +2348,13 @@ defmodule SpitfireTest do
              end)
     end
 
+    test "fn -> followed by closing delimiter does not hang" do
+      assert {:error, _ast, _errors} = Spitfire.parse("fn ->)")
+      assert {:error, _ast, _errors} = Spitfire.parse("fn ->")
+      assert {:error, _ast, _errors} = Spitfire.parse("Enum.map(fn ->)")
+      assert {:error, _ast, _errors} = Spitfire.parse("fn ->\n)")
+    end
+
     test "missing bitstring brackets" do
       code = """
       <<one::