Make blank/empty comparisons invariant to ActiveSupport

- Implement liquid_blank? and liquid_empty? methods in Condition
  to emulate ActiveSupport's behavior when it's not loaded
- This ensures templates like `{% if x == blank %}` work identically
  whether ActiveSupport is loaded or not
- Update liquid-spec adapters for new API (ctx parameter)
- Add rake spec task for running liquid-spec matrix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

spec/ruby_liquid.rb

@@ -13,15 +13,16 @@ LiquidSpec.configure do |config|
 end
 
 # Compile a template string into a Liquid::Template
-LiquidSpec.compile do |source, options|
+LiquidSpec.compile do |ctx, source, options|
   Liquid::Template.parse(source, **options)
 end
 
 # Render a compiled template with the given context
+# @param ctx [Hash] adapter context (unused)
 # @param template [Liquid::Template] compiled template
 # @param assigns [Hash] environment variables
 # @param options [Hash] :registers, :strict_errors, :exception_renderer
-LiquidSpec.render do |template, assigns, options|
+LiquidSpec.render do |ctx, template, assigns, options|
   registers = Liquid::Registers.new(options[:registers] || {})
 
   context = Liquid::Context.build(

spec/ruby_liquid_with_active_support.rb

@@ -14,15 +14,16 @@ LiquidSpec.configure do |config|
 end
 
 # Compile a template string into a Liquid::Template
-LiquidSpec.compile do |source, options|
+LiquidSpec.compile do |ctx, source, options|
   Liquid::Template.parse(source, **options)
 end
 
 # Render a compiled template with the given context
+# @param ctx [Hash] adapter context (unused)
 # @param template [Liquid::Template] compiled template
 # @param assigns [Hash] environment variables
 # @param options [Hash] :registers, :strict_errors, :exception_renderer
-LiquidSpec.render do |template, assigns, options|
+LiquidSpec.render do |ctx, template, assigns, options|
   registers = Liquid::Registers.new(options[:registers] || {})
 
   context = Liquid::Context.build(