One way to avoid the leak would be using weak references

# declare stuff package stuff here ...
use WeakRef;

sub new {
    my($class, $session) = @_
    my $self = { };
    bless($self, $class);
    weaken($self->{'session'} = $session);
}
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So when your instance goes out of scope it's refcount should reach 0 and be released.
HTH

broquaint