Support cursors on readonly queries

This adds `:declare`, `:fetch`, `:move`, and `:close` to allowed queries
when `while_preventing_writes` is set. I didn't support `:open` because
AFAICT `:declar` implcitly opens a cursor and all of my attempts to
write `@connection.execute("OPEN cur_ex")` threw a syntax error on
`OPEN`. It seems like open isn't supported with the client.

Fixes: #37960

activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb

@@ -68,7 +68,7 @@ def query(sql, name = nil) #:nodoc:
         end
 
         READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp(
-          :set, :show
+          :close, :declare, :fetch, :move, :set, :show
         ) # :nodoc:
         private_constant :READ_QUERY
 

activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb

@@ -457,6 +457,19 @@ def test_doesnt_error_when_a_read_query_with_leading_chars_is_called_while_preve
         end
       end
 
+      def test_doesnt_error_when_a_read_query_with_cursors_is_called_while_preventing_writes
+        with_example_table do
+          @connection_handler.while_preventing_writes do
+            @connection.transaction do
+              assert_equal [], @connection.execute("DECLARE cur_ex CURSOR FOR SELECT * FROM ex").entries
+              assert_equal [], @connection.execute("FETCH cur_ex").entries
+              assert_equal [], @connection.execute("MOVE cur_ex").entries
+              assert_equal [], @connection.execute("CLOSE cur_ex").entries
+            end
+          end
+        end
+      end
+
       private
         def with_example_table(definition = "id serial primary key, number integer, data character varying(255)", &block)
           super(@connection, "ex", definition, &block)