docs: clarify how mutmut copies files

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: deviantintegral

tests/test_b2c_login.py

@@ -1818,6 +1818,8 @@ async def test_set_cookie_header_case_insensitive(self):
         # And the results should be identical for any casing of the key.
         assert headers.getall("set-cookie") == values_mixed
         assert headers.getall("SET-COOKIE") == values_mixed
+
+
 class TestB2cLoginLogCallMutants:
     """Tests that kill logging-related mutants inside b2c_login_with_credentials.
 

tests/test_protocol.py

@@ -1599,8 +1599,8 @@ class TestMakeHeaderSignedUnsigned:
     so passing payload_size >= 128 would raise struct.error with 'hb'
     but succeed with 'HB'.
 
-    We call through the module attribute so that mutmut's monkey-patching
-    is picked up (a bare import caches the original function reference).
+    These tests exercise payload_size boundary conditions to
+    distinguish the original implementation from the mutant.
     """
 
     def test_large_payload_size_succeeds(self):