Reset plsql.activerecord_class after ActiveRecord connection examples

The ActiveRecord connection describe block bound the global plsql
schema to ActiveRecord via plsql.activerecord_class= in before(:each)
but never reset it. Because oci_connection.ora_date_to_ruby_date
consults plsql.default_timezone (a singleton on the global plsql
schema), and that accessor returns ActiveRecord.default_timezone
when an AR class is bound, every subsequent test that read DATE
values back through any OCI connection saw UTC values instead of
the local-time defaults. The connection-level
"should parse PL/SQL procedure call ... and get bind parameter
value" example then asserted equality between a local Time and the
UTC round-trip and failed.

Reset plsql.activerecord_class to nil in after(:all) so other
describe blocks observe a fresh, non-AR-bound plsql singleton.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yahonda

spec/plsql/schema_spec.rb

@@ -193,6 +193,10 @@ class TestModel < TestBaseModel
     end
   end
 
+  after(:all) do
+    plsql.activerecord_class = nil
+  end
+
   before(:each) do
     plsql.activerecord_class = ActiveRecord::Base
   end