Fix memory leak in AWAIT_ON_READY

The original implementation used _finally(), which created multiple
intermediate promise objects.  These weren't settled until the event
loop stopped, creating a memory leak and significant delay on stop.

Simplified AWAIT_ON_READY to directly register callbacks without
intermediate objects, eliminating the leak while maintaining correct
functionality.  This will also be quicker.

Fixes #2220

Author: TFBW

lib/Mojo/Promise.pm

@@ -37,7 +37,9 @@ sub AWAIT_NEW_FAIL { _await('reject',  @_) }
 sub AWAIT_ON_CANCEL { }
 
 sub AWAIT_ON_READY {
-  shift->_finally(0, @_)->catch(sub { });
+  my ($self, $cb) = @_;
+  push @{$self->{resolve}}, $cb;
+  push @{$self->{reject}},  $cb;
 }
 
 sub AWAIT_WAIT {