refactor(test): modernize waiter code with Python idioms and robust tests

why: Improve code readability, maintainability and reliability through modern Python patterns and enhanced test coverage for edge cases.

what:
- Replace for-loops with next() and generator expressions
- Use walrus operator (:=) to reduce nesting in conditional code
- Remove redundant conditional code in retry_extended.py
- Fix incorrect test expectations for invalid prompt handling
- Add negative test cases for line range validation
- Update docstrings for better clarity and accuracy

refs: #sourcery-ai

Author: tony

src/libtmux/test/retry_extended.py

@@ -15,12 +15,8 @@
 logger = logging.getLogger(__name__)
 
 if t.TYPE_CHECKING:
-    import sys
     from collections.abc import Callable
 
-    if sys.version_info >= (3, 11):
-        pass
-
 
 def retry_until_extended(
     fun: Callable[[], bool],

src/libtmux/test/waiter.py

@@ -1090,7 +1090,7 @@ def _contains_match(
     content : list[str]
         Lines of content to check
     pattern : str
-        Pattern to look for within the content
+        String to check for in content
 
     Returns
     -------
@@ -1100,12 +1100,10 @@ def _contains_match(
     content_str = "\n".join(content)
     if pattern in content_str:
         # Find which line contains the match
-        for i, line in enumerate(content):
-            if pattern in line:
-                return True, pattern, i
-        # If we somehow didn't find it in any individual line but it was in the
-        # joined string
-        return True, pattern, None
+        return next(
+            ((True, pattern, i) for i, line in enumerate(content) if pattern in line),
+            (True, pattern, None),
+        )
     return False, None, None
 
 
@@ -1129,16 +1127,18 @@ def _regex_match(
     """
     content_str = "\n".join(content)
     regex = pattern if isinstance(pattern, re.Pattern) else re.compile(pattern)
-    match = regex.search(content_str)
 
-    if match:
+    if match := regex.search(content_str):
         matched_text = match.group(0)
         # Try to find which line contains the match
-        for i, line in enumerate(content):
-            if regex.search(line):
-                return True, matched_text, i
-        # If no specific line found but match exists in joined content
-        return True, matched_text, None
+        return next(
+            (
+                (True, matched_text, i)
+                for i, line in enumerate(content)
+                if regex.search(line)
+            ),
+            (True, matched_text, None),
+        )
 
     return False, None, None
 
@@ -1159,15 +1159,17 @@ def _match_regex_across_lines(
     """
     content_str = "\n".join(content)
     regex = pattern if isinstance(pattern, re.Pattern) else re.compile(pattern)
-    match = regex.search(content_str)
 
-    if match:
+    if match := regex.search(content_str):
         matched_text = match.group(0)
         # Try to find which line contains the match
-        for i, line in enumerate(content):
-            if regex.search(line):
-                return True, matched_text, i
-        # If no specific line found but match exists in joined content
-        return True, matched_text, None
+        return next(
+            (
+                (True, matched_text, i)
+                for i, line in enumerate(content)
+                if regex.search(line)
+            ),
+            (True, matched_text, None),
+        )
 
     return False, None, None