Address liquid-spec issues without ActiveSupport loaded

Implement ActiveSupport-compatible behaviors internally so Liquid works
correctly without ActiveSupport being loaded:

1. String first/last via property access (name.first, name.last)
   - VariableLookup now handles string[0] and string[-1] for first/last

2. String first/last via filters (name | first, name | last)
   - StandardFilters#first and #last now handle strings

3. blank?/empty? comparisons for types without these methods
   - Condition now implements liquid_blank? and liquid_empty? internally
   - blank? matches ActiveSupport: nil, false, empty/whitespace strings,
     empty arrays/hashes are all blank
   - empty? checks length == 0 only (whitespace is NOT empty)

This fixes spec failures for templates like:
- {{ name.first }} / {{ name | first }} on strings
- {% if x == blank %} for whitespace strings, empty hashes/arrays
- {% case ' ' %}{% when blank %} matching whitespace

lib/liquid/condition.rb

@@ -113,24 +113,66 @@ module Liquid
 
     def equal_variables(left, right)
       if left.is_a?(MethodLiteral)
-        if right.respond_to?(left.method_name)
-          return right.send(left.method_name)
-        else
-          return nil
-        end
+        return call_method_literal(left, right)
       end
 
       if right.is_a?(MethodLiteral)
-        if left.respond_to?(right.method_name)
-          return left.send(right.method_name)
-        else
-          return nil
-        end
+        return call_method_literal(right, left)
       end
 
       left == right
     end
 
+    def call_method_literal(literal, value)
+      method_name = literal.method_name
+
+      # If the object responds to the method, use it
+      if value.respond_to?(method_name)
+        return value.send(method_name)
+      end
+
+      # Implement blank?/empty? for common types that don't have it
+      # (ActiveSupport adds these, but Liquid should work without it)
+      case method_name
+      when :blank?
+        liquid_blank?(value)
+      when :empty?
+        liquid_empty?(value)
+      else
+        nil
+      end
+    end
+
+    # Implement blank? semantics matching ActiveSupport
+    def liquid_blank?(value)
+      case value
+      when NilClass, FalseClass
+        true
+      when TrueClass, Numeric
+        false
+      when String
+        # Blank if empty or whitespace only
+        value.empty? || value.match?(/\A\s*\z/)
+      when Array, Hash
+        value.empty?
+      else
+        # Fall back to empty? if available, otherwise false
+        value.respond_to?(:empty?) ? value.empty? : false
+      end
+    end
+
+    # Implement empty? semantics
+    def liquid_empty?(value)
+      case value
+      when NilClass
+        true
+      when String, Array, Hash
+        value.empty?
+      else
+        value.respond_to?(:empty?) ? value.empty? : false
+      end
+    end
+
     def interpret_condition(left, right, op, context)
       # If the operator is empty this means that the decision statement is just
       # a single variable. We can just poll this variable from the context and

lib/liquid/standardfilters.rb

@@ -768,6 +768,7 @@ module Liquid
     # @liquid_syntax array | first
     # @liquid_return [untyped]
     def first(array)
+      return array[0] if array.is_a?(String)
       array.first if array.respond_to?(:first)
     end
 
@@ -779,6 +780,7 @@ module Liquid
     # @liquid_syntax array | last
     # @liquid_return [untyped]
     def last(array)
+      return array[-1] if array.is_a?(String)
       array.last if array.respond_to?(:last)
     end
 

lib/liquid/variable_lookup.rb

@@ -70,6 +70,10 @@ module Liquid
         elsif lookup_command?(i) && object.respond_to?(key)
           object = object.send(key).to_liquid
 
+        # Handle string first/last like ActiveSupport does (returns first/last character)
+        elsif lookup_command?(i) && object.is_a?(String) && (key == "first" || key == "last")
+          object = key == "first" ? object[0] : object[-1]
+
           # No key was present with the desired value and it wasn't one of the directly supported
           # keywords either. The only thing we got left is to return nil or
           # raise an exception if `strict_variables` option is set to true