test: review follow-up coverage for --fuzzy

Unit (CLI): --fuzzy --no-incremental (either order) stays a valid plain-mode
config -- no forced handshake, no delta implication; --fuzzy --no-delta stays
covered.

Integration (TestFuzzy):
- worthless basis: a sibling that passes the name+size gates but shares no
  blocks makes the sender reply STATUS_NEXT; the whole file is consumed inside
  the delta handshake with byte-exact output (no protocol desync).
- non-displacement: an existing exact-path destination file INSIDE the delta
  size bounds (same size, different content, older mtime) is used as the delta
  basis instead of a byte-identical similar sibling (whole-file wire cost).
- asymmetric bases: basis larger than source (prefix reuse) and basis smaller
  than source (appended tail as literals) both reconstruct byte-exactly with a
  small delta.
- --no-fuzzy end-to-end equals the no-flag whole-file behavior.
CountingProxy closes its listener socket (fd hygiene).

tests/integration/common.py

@@ -106,6 +106,7 @@ class CountingProxy:
                 server_sock = socket.create_connection(("127.0.0.1", self.target_port),
                                                        timeout=10)
             except OSError:
+                self._listener.close()
                 return
             c2s, s2c = [0], [0]
             a = threading.Thread(target=self._pump, args=(client_sock, server_sock, c2s))
@@ -116,6 +117,7 @@ class CountingProxy:
             b.join()
             self.client_to_server = c2s[0]
             self.server_to_client = s2c[0]
+            self._listener.close()
 
         thread = threading.Thread(target=serve)
         thread.start()