Improve render performance of large wiki pages

Compile often used regexps only once outside of the loop.

This commit improves the performance of large wiki pages with many, many references.

lib/banzai/filter/abstract_reference_filter.rb

@@ -100,6 +100,11 @@ module Banzai
         ref_pattern = object_class.reference_pattern
         link_pattern = object_class.link_reference_pattern
 
+        # Compile often used regexps only once outside of the loop
+        ref_pattern_anchor = /\A#{ref_pattern}\z/
+        link_pattern_start = /\A#{link_pattern}/
+        link_pattern_anchor = /\A#{link_pattern}\z/
+
         nodes.each do |node|
           if text_node?(node) && ref_pattern
             replace_text_when_pattern_matches(node, ref_pattern) do |content|
@@ -108,7 +113,7 @@ module Banzai
 
           elsif element_node?(node)
             yield_valid_link(node) do |link, inner_html|
-              if ref_pattern && link =~ /\A#{ref_pattern}\z/
+              if ref_pattern && link =~ ref_pattern_anchor
                 replace_link_node_with_href(node, link) do
                   object_link_filter(link, ref_pattern, link_content: inner_html)
                 end
@@ -118,7 +123,7 @@ module Banzai
 
               next unless link_pattern
 
-              if link == inner_html && inner_html =~ /\A#{link_pattern}/
+              if link == inner_html && inner_html =~ link_pattern_start
                 replace_link_node_with_text(node, link) do
                   object_link_filter(inner_html, link_pattern, link_reference: true)
                 end
@@ -126,7 +131,7 @@ module Banzai
                 next
               end
 
-              if link =~ /\A#{link_pattern}\z/
+              if link =~ link_pattern_anchor
                 replace_link_node_with_href(node, link) do
                   object_link_filter(link, link_pattern, link_content: inner_html, link_reference: true)
                 end