Fix excessive logging by instrumentation plugin

It happens when there're more than one container using the same gateway. This issue is already fixed in the main branch, I'll add the spec there, though

lib/rom/plugins/relation/sql/instrumentation.rb

@@ -35,6 +35,8 @@ module Instrumentation
             db_notifications = relations.values.map { |r| [r.dataset.db, r.notifications] }.uniq.to_h
 
             db_notifications.each do |db, notifications|
+              next if db.respond_to?(:rom_instrumentation?)
+
               instrumenter = Instrumenter.new(db.database_type, notifications)
               db.extend(instrumenter)
             end
@@ -56,6 +58,8 @@ class Instrumenter < Module
 
             # @api private
             def initialize(name, notifications)
+              super()
+
               @name = name
               @notifications = notifications
               define_log_connection_yield
@@ -68,6 +72,8 @@ def define_log_connection_yield
               name = self.name
               notifications = self.notifications
 
+              define_method(:rom_instrumentation?) { true }
+
               define_method(:log_connection_yield) do |*args, &block|
                 notifications.instrument(:sql, name: name, query: args[0]) do
                   super(*args, &block)

spec/unit/relation/instrument_spec.rb

@@ -64,4 +64,30 @@ def instrument(*args, &block)
     expect(notifications.logs).
       to include([:sql, name: :sqlite, query: "SELECT count(*) AS 'count' FROM `users` LIMIT 1"])
   end
+
+  context 'two containers with shared gateway' do
+    let(:conf_alt) { TestConfiguration.new(:sql, conn) }
+
+    let(:container_alt) { ROM.container(conf_alt) }
+
+    before do
+      conf_alt.plugin(:sql, relations: :instrumentation)
+
+      conf_alt.relation(:users) do
+        schema(infer: true)
+      end
+
+      container_alt
+    end
+
+    it 'instruments relation materialization but does it once' do
+      relation.to_a
+
+      entries = notifications.logs.count do |log|
+        log.eql?([:sql, name: :sqlite, query: relation.dataset.sql])
+      end
+
+      expect(entries).to be(1)
+    end
+  end
 end