perf: replace method(:region_for) with block in BrowserHelpers

Avoids allocating a Method object on every call to
all_visible_regions_for. Use a simple block instead.

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

Author: pftg

lib/capybara/screenshot/diff/browser_helpers.rb

@@ -85,7 +85,7 @@ def self.blur_from_focused_element
       JS
 
       def self.all_visible_regions_for(selector)
-        BrowserHelpers.session.all(selector, visible: true).map(&method(:region_for))
+        BrowserHelpers.session.all(selector, visible: true).map { |el| region_for(el) }
       end
 
       def self.region_for(element)