add site pages cache

This cache allows template helpers to quickly get at the entire site's page list
so that they can build navigations or produce metadata about the site.

lib/Statocles/Site.pm

@@ -339,6 +339,20 @@ has _write_deploy => (
     clearer => '_clear_write_deploy',
 );
 
+=attr pages
+
+A cache of all the pages that the site contains. This is generated
+during the C<build> phase and is available to all the templates
+while they are being rendered.
+
+=cut
+
+has pages => (
+    is => 'rw',
+    isa => ArrayRef[ConsumerOf['Statocles::Page']],
+    default => sub { [] },
+);
+
 =method BUILD
 
 Register this site as the global site.
@@ -513,7 +527,9 @@ sub build {
         pages => \@pages,
     );
 
-    # @pages should not change after this, because it is used in the render loop below.
+    # @pages should not change after this, because it is being cached
+    $self->pages( \@pages );
+
     $self->emit(
         'before_build_write',
         class => 'Statocles::Event::Pages',

t/site/build_and_deploy.t

@@ -41,6 +41,8 @@ sub test_base_url {
 }
 
 subtest 'build' => sub {
+    cmp_deeply $site->pages, [], 'page cache is empty until a build';
+
     $site->build;
 
     my @pages;
@@ -67,6 +69,9 @@ subtest 'build' => sub {
         }
     };
 
+    # Add 2 pages for robots.txt and sitemap.xml
+    is scalar @{ $site->pages }, scalar @pages + 2, 'cached page count is correct';
+
     subtest 'build deletes files before building' => sub {
         $build_dir->child( 'DELETE_ME' )->spew( "This should be deleted" );
         $site->build;