fix(tests[waiter]): replace fixed sleep with wait_for_pane_content

why: test_wait_for_pane_content_exact_match_detailed used time.sleep(0.1)
to wait for content to appear after send_keys, but on tmux 3.6+ that
interval is sometimes too short — leading to intermittent failures
when capture_pane returned an empty pane and the subsequent assertion
triggered. Surfaced by running the suite with --reruns=0.
what:
- replace time.sleep(0.1) with a wait_for_pane_content(CONTAINS) call
  that waits up to 2.0s for the unique test string to appear
- this is deterministic and uses the very feature under test, so the
  test no longer relies on timing for setup

Author: tony

tests/_internal/test_waiter.py

@@ -1852,8 +1852,15 @@ def test_wait_for_pane_content_exact_match_detailed(wait_pane: Pane) -> None:
     # Send a unique string that we can test with an exact match
     wait_pane.send_keys("UNIQUE_TEST_STRING_123", literal=True)
 
-    # Small delay to allow tmux to flush content (needed for older versions like 3.1b)
-    time.sleep(0.1)
+    # Wait deterministically for the string to appear in the pane
+    # rather than sleeping a fixed interval (flaky on slower tmux versions)
+    wait_for_pane_content(
+        wait_pane,
+        "UNIQUE_TEST_STRING_123",
+        ContentMatchType.CONTAINS,
+        timeout=2.0,
+        interval=0.05,
+    )
 
     # Get the current content to work with
     content = wait_pane.capture_pane()