Switch default connection pool to timed_queue on Ruby 3.4+

This gives about a whole year for Sequel users to test this with
Ruby 3.4 previews, and it ensures Sequel will not switch the
connection pool type for anything using a released version of
Ruby.

Assuming no problems are reported, in Sequel 6, or potentially
earlier, we'll switch this from 3.4+ to 3.2+.

CHANGELOG

@@ -1,5 +1,7 @@
 === master
 
+* Switch default connection pool to timed_queue on Ruby 3.4+ (jeremyevans)
+
 * Support on_duplicate_columns={raise,warn} parameter in connection URL when using duplicate_columns_handler extension (jeremyevans)
 
 * Add transaction_connection_validator extension for retrying transactions on new connection if ther is a disconnect error when starting transaction (jeremyevans)

lib/sequel/connection_pool.rb

@@ -70,8 +70,10 @@ def connection_pool_class(opts)
       else
         pc = if opts[:single_threaded]
           opts[:servers] ? :sharded_single : :single
-        #elsif RUBY_VERSION >= '3.2' # SEQUEL6 or maybe earlier
-        #  opts[:servers] ? :sharded_timed_queue : :timed_queue
+        # :nocov:
+        elsif RUBY_VERSION >= '3.4' # SEQUEL6 or maybe earlier switch to 3.2
+          opts[:servers] ? :sharded_timed_queue : :timed_queue
+        # :nocov:
         else
           opts[:servers] ? :sharded_threaded : :threaded
         end