Fix the antispam test: pin the rules it scores against, stop live Pyzor

It failed everywhere but upstream's machines, for two reasons:

- The spam rules, which carry every score, came from a path on an
  upstream developer's own disk. Without SPAM_RULES_URL none loaded, every
  score was 0.00 and the combined case came out ham instead of spam at
  13.70. The published rules of spam-filter v3.0.2 are now pinned beside
  the test cases (Apache-2.0 or MIT, taken as MIT; in THIRD-PARTY.md).
  SPAM_RULES_URL still overrides.
- The first combined case expects a Pyzor hit, and its digest (that of an
  empty body) wasn't among the three the test mode answers, so it went to
  a public Pyzor server: it failed offline and would drift with that
  server's counts. Test mode now answers every digest from a fixed table,
  with the empty body's added, and never reaches the network.

The test passes online and offline, alone and with the rest of the SMTP
tests. queue_retry, unrelated, still fails when it runs after the others
in one process, though it passes alone every time.

THIRD-PARTY.md

@@ -24,6 +24,7 @@ carry their own license files.
 | `crates/common/src/network/acme/directory.rs`, `crates/common/src/network/acme/jose.rs`, `crates/common/src/network/acme/order.rs` | [rustls-acme](https://github.com/FlorianUekermann/rustls-acme) (MIT or Apache-2.0) | Copyright (c) Florian Uekermann |
 | `crates/types/src/id.rs` | [crockford](https://github.com/archer884/crockford) (MIT or Apache-2.0) | Copyright (c) 2017 J/A <archer884@gmail.com> |
 | `crates/nlp/src/tokenizers/types.rs` | test cases from [linkify](https://github.com/robinst/linkify) (MIT or Apache-2.0) | Copyright (c) 2017 Robin Stocker |
+| `tests/resources/smtp/antispam/spam-filter-rules.json.gz` | the published rules of [spam-filter](https://github.com/stalwartlabs/spam-filter) v3.0.2, unmodified, for the spam filter's tests (MIT or Apache-2.0) | Copyright (C) 2024, Stalwart Labs LLC |
 
 Each notice above applies with this permission notice: