fix: freeze options hash and widen rescue in files_identical?

Address PR review feedback:
- Freeze options instead of sharing mutable reference
- Add IOError to rescue alongside SystemCallError

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pftg

lib/capybara/screenshot/diff/image_compare.rb

@@ -46,7 +46,7 @@ def initialize(image_path, base_image_path, options = {})
 
           ensure_files_exist!
 
-          @driver_options = options
+          @driver_options = options.freeze
           @driver = Drivers.for(@driver_options)
         end
 
@@ -184,7 +184,7 @@ def images_exist?
         # Check if files are identical by content
         def files_identical?(file1, file2)
           FileUtils.compare_file(file1, file2)
-        rescue SystemCallError
+        rescue SystemCallError, IOError
           false
         end
       end