refactor(qa): Avoid unnecessary string operations

print_log was recalculated every 0.05s in assert_debug_log(), even during successful circumstances - changed to only be computed upon failure.

Simplified terminology from "(does not) partially match(es)" to "(not) found in" since it seems to reference the first function having used regular expression matching, while it always escaped the search strings (see parent commit). (Simplified grammar also avoids issues with singular/plural "was/were not found").

test/functional/test_framework/test_node.py

@@ -550,6 +550,9 @@ class TestNode():
         time_end = time.time() + timeout * self.timeout_factor
         prev_size = self.debug_log_size(encoding="utf-8")  # Must use same encoding that is used to read() below
 
+        def join_log(log):
+            return " - " + "\n - ".join(log.splitlines())
+
         yield
 
         while True:
@@ -557,10 +560,10 @@ class TestNode():
             with open(self.debug_log_path, encoding="utf-8", errors="replace") as dl:
                 dl.seek(prev_size)
                 log = dl.read()
-            print_log = " - " + "\n - ".join(log.splitlines())
             for unexpected_msg in unexpected_msgs:
                 if unexpected_msg in log:
-                    self._raise_assertion_error('Unexpected message "{}" partially matches log:\n\n{}\n\n'.format(unexpected_msg, print_log))
+                    self._raise_assertion_error(f'Unexpected message "{unexpected_msg}" '
+                                                f'found in log:\n\n{join_log(log)}\n\n')
             for expected_msg in expected_msgs:
                 if expected_msg not in log:
                     found = False
@@ -569,7 +572,8 @@ class TestNode():
             if time.time() >= time_end:
                 break
             time.sleep(0.05)
-        self._raise_assertion_error('Expected messages "{}" does not partially match log:\n\n{}\n\n'.format(str(expected_msgs), print_log))
+        self._raise_assertion_error(f'Expected message(s) {expected_msgs!s} '
+                                    f'not found in log:\n\n{join_log(log)}\n\n')
 
     @contextlib.contextmanager
     def busy_wait_for_debug_log(self, expected_msgs, timeout=60):
@@ -601,9 +605,8 @@ class TestNode():
             # No sleep here because we want to detect the message fragment as fast as
             # possible.
 
-        self._raise_assertion_error(
+        self._raise_assertion_error(f'Expected message(s) {expected_msgs!s} '
-            'Expected messages "{}" does not partially match log:\n\n{}\n\n'.format(
+                                    f'not found in log:\n\n{print_log}\n\n')
-                str(expected_msgs), print_log))
 
     @contextlib.contextmanager
     def wait_for_new_peer(self, timeout=5):