Remove lock_thread on connection pool

The commit that added
lock_thread (f638085) notes that
> Transaction management is largely ripped straight out of
> test_fixtures.rb in Rails

The commit that adds lock_thread in Rails --
rails/rails@d6466be
-- has some helpful context:
> When a system test starts Puma spins up one thread and Capybara spins
> up another thread. Because of this when tests are run the database
> cannot see what was inserted into the database on teardown. This is
> because there are two threads using two different connections.

> This change uses the statement cache to lock the threads to using a
> single connection ID instead of each not being able to see each other.

So lock_thread exists because there are two different threads -- Puma
and Capybara -- trying to access the same database but not necessarily
seeing the same thing. But! cypress-rails doesn't use Capybara, and more
importantly, it doesn't use tests or a test runner written in Ruby at
all, so there's only _one_ thread trying to use the database. So we
don't need all this thread locking stuff. So let's remove it to make
things more compatible with Rails 7.2.

Author: rosston

lib/cypress-rails/manages_transactions.rb

@@ -10,7 +10,6 @@ def begin_transaction
       @connections = gather_connections
       @connections.each do |connection|
         connection.begin_transaction joinable: false, _lazy: false
-        connection.pool.lock_thread = true
       end
 
       # When connections are established in the future, begin a transaction too
@@ -26,7 +25,6 @@ def begin_transaction
 
           if connection && !@connections.include?(connection)
             connection.begin_transaction joinable: false, _lazy: false
-            connection.pool.lock_thread = true
             @connections << connection
           end
         end
@@ -42,7 +40,6 @@ def rollback_transaction
 
       @connections.each do |connection|
         connection.rollback_transaction if connection.transaction_open?
-        connection.pool.lock_thread = false
       end
       @connections.clear