Apply optimizations to merge request reference rendering

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/271242

* Short-circuit cross_namespace check
* Use memoized result of the full_path

Changelog: performance

app/models/project.rb

@@ -2663,7 +2663,7 @@ class Project < ApplicationRecord
   def cross_namespace_reference?(from)
     case from
     when Project
-      namespace != from.namespace
+      namespace_id != from.namespace_id
     when Namespace
       namespace != from
     when User

ee/changelogs/unreleased/271242_optimize_merge_request_filter.yml

+---
+title: Apply optimizations to merge request reference rendering
+merge_request: 60500
+author:
+type: performance

ee/spec/models/ee/vulnerability_spec.rb

@@ -616,7 +616,7 @@ RSpec.describe Vulnerability do
       end
 
       context 'when cross-project in different namespace' do
-        let(:another_namespace) { build(:namespace, path: 'another-namespace') }
+        let(:another_namespace) { build(:namespace, id: non_existing_record_id, path: 'another-namespace') }
         let(:another_namespace_project) { build(:project, path: 'another-project', namespace: another_namespace) }
 
         it 'returns complete path to the vulnerability' do

lib/banzai/filter/references/merge_request_reference_filter.rb

@@ -58,7 +58,7 @@ module Banzai
         end
 
         def data_attributes_for(text, parent, object, **data)
-          super.merge(project_path: parent.full_path, iid: object.iid, mr_title: object.title)
+          super.merge(project_path: current_parent_path, iid: object.iid, mr_title: object.title)
         end
 
         private

spec/models/design_management/design_spec.rb

@@ -512,7 +512,7 @@ RSpec.describe DesignManagement::Design do
   end
 
   describe '#to_reference' do
-    let(:namespace) { build(:namespace, path: 'sample-namespace') }
+    let(:namespace) { build(:namespace, id: non_existing_record_id, path: 'sample-namespace') }
     let(:project)   { build(:project, name: 'sample-project', namespace: namespace) }
     let(:group)     { create(:group, name: 'Group', path: 'sample-group') }
     let(:issue)     { build(:issue, iid: 1, project: project) }

spec/models/issue_spec.rb

@@ -297,7 +297,7 @@ RSpec.describe Issue do
       end
 
       context 'when cross-project in different namespace' do
-        let(:another_namespace) { build(:namespace, path: 'another-namespace') }
+        let(:another_namespace) { build(:namespace, id: non_existing_record_id, path: 'another-namespace') }
         let(:another_namespace_project) { build(:project, path: 'another-project', namespace: another_namespace) }
 
         it 'returns complete path to the issue' do