use getbyte dispatch instead of start_with? in parse_for_document

lib/liquid/block_body.rb

@@ -175,11 +175,17 @@ module Liquid
       end
     end
 
+    OPEN_CURLEY_BYTE = 123 # '{'.ord
+    PERCENT_BYTE = 37 # '%'.ord
+
     private def parse_for_document(tokenizer, parse_context, &block)
       while (token = tokenizer.shift)
         next if token.empty?
-        case
-        when token.start_with?(TAGSTART)
+
+        first_byte = token.getbyte(0)
+        if first_byte == OPEN_CURLEY_BYTE
+          second_byte = token.getbyte(1)
+          if second_byte == PERCENT_BYTE
             whitespace_handler(token, parse_context)
             parsed = BlockBody.parse_tag_token(token)
             unless parsed
@@ -206,10 +212,19 @@ module Liquid
             new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
             @blank &&= new_tag.blank?
             @nodelist << new_tag
-        when token.start_with?(VARSTART)
+          elsif second_byte == OPEN_CURLEY_BYTE
             whitespace_handler(token, parse_context)
             @nodelist << create_variable(token, parse_context)
             @blank = false
+          else
+            # Fallback: text token starting with '{'
+            if parse_context.trim_whitespace
+              token.lstrip!
+            end
+            parse_context.trim_whitespace = false
+            @nodelist << token
+            @blank &&= token.match?(WhitespaceOrNothing)
+          end
         else
           if parse_context.trim_whitespace
             token.lstrip!