Fix find_by_kind Enumerator compatibility in FFI visitor

The monkey-patched find_by_kind returns an Enumerator (not Array),
so .empty? doesn't work. Use find_first_by_kind instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cfis

lib/ruby-bindgen/visitors/ffi/ffi.rb

@@ -98,7 +98,7 @@ def render_children(cursor, indentation: 0, separator: "\n", terminator: "", str
 
       def visit_callback(name, parameters, type)
         parameter_types = parameters.map do |parameter|
-          if !parameter.find_by_kind(false, :cursor_type_ref).empty? && parameter.type.is_a?(::FFI::Clang::Types::Pointer)
+          if parameter.find_first_by_kind(false, :cursor_type_ref) && parameter.type.is_a?(::FFI::Clang::Types::Pointer)
             ":pointer"
           else
             figure_ffi_type(parameter.type, :callback)