refactor: replace 0.step with loop in StableScreenshoter

Simpler loop construct. Move sleep after checks instead of
guarding with i == 0 — same behavior, clearer intent.

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

Author: pftg

lib/capybara/screenshot/diff/stable_screenshoter.rb

@@ -61,14 +61,13 @@ def take_stable_screenshot(snapshot)
           # Cleanup all previous attempts for sure
           snapshot.cleanup_attempts!
 
-          0.step do |i|
-            # FIXME: it should be wait, and wait should be replaced with stability_time_limit
-            sleep(stability_time_limit) unless i == 0 # test prev_attempt_path is nil
-
+          loop do
             attempt_next_screenshot(snapshot)
 
             return true if attempt_successful?(snapshot)
             return false if timeout?(deadline_at)
+
+            sleep(stability_time_limit)
           end
         end