tidy-up: miscellaneous

- badwords: replace stray synonyms with 'null-terminator'.
- tests/FILEFORMAT.md: tidy up feature descriptions.
- printf: replace stray `%i` masks with `%d` for consistency.
- pytest: add comments for empty excepts to try silencing GitHub CodeQL
  warnings.
- tool1394, unit1675: merge nested `if`s.
- dnscache: fix typo in comment.
- fix whitespace, indent and newlines.

Closes #21921

tests/http/test_05_errors.py

@@ -197,6 +197,7 @@ class TestErrors:
                     conn.recv(1)  # wait for ClientHello
                     conn.close()
                 except Exception:
+                    # ignore expected socket error
                     pass
 
             t = threading.Thread(target=accept_and_close)