test: add coverage for statement resource cleanup

Note that the unclosed statement object test fails at the moment.

test/test_resource_cleanup.rb

@@ -0,0 +1,27 @@
+require "helper"
+
+module SQLite3
+  # these tests will cause ruby_memcheck to report a leak if we're not cleaning up resources
+  class TestResourceCleanup < SQLite3::TestCase
+    def test_cleanup_unclosed_database_object
+      100.times do
+        SQLite3::Database.new(':memory:')
+      end
+    end
+
+    def test_cleanup_unclosed_statement_object
+      100.times do
+        db = SQLite3::Database.new(':memory:')
+        db.execute('create table foo(text BLOB)')
+        db.prepare('select * from foo')
+      end
+    end
+
+    # def test_cleanup_unclosed_resultset_object
+    #   db = SQLite3::Database.new(':memory:')
+    #   db.execute('create table foo(text BLOB)')
+    #   stmt = db.prepare('select * from foo')
+    #   stmt.execute
+    # end
+  end
+end