Bound crack memory: cap wordlist sort, chunk target loading

- prepare_candidates: use sort -S 1G --parallel 4 (was unbounded, OOM-prone
  on large --passwords-from datasets)
- crack: add --max-hashes to stream large hash files in bounded chunks, so the
  in-RAM target index no longer scales with the whole input
- docs + regression test for chunked cracking

tests/crack_test.py

@@ -72,6 +72,29 @@ class CrackTest(unittest.TestCase):
             self.assertEqual(1, total)
             self.assertEqual([b"[email protected]:reused"], out.read_bytes().splitlines())
 
+    def test_crack_chunks_hash_file(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            hashes = Path(tmp) / "hashes.txt"
+            hashes.write_bytes(
+                b"[email protected]:" + hashlib.md5(b"hunter2").hexdigest().encode() + b"\n"
+                b"[email protected]:" + hashlib.sha1(b"secret").hexdigest().encode() + b"\n"
+            )
+            wordlist = Path(tmp) / "words.txt"
+            wordlist.write_bytes(b"hunter2\nsecret\n")
+            out = Path(tmp) / "cracked.txt"
+            total = crack(
+                str(hashes),
+                str(out),
+                wordlists=[str(wordlist)],
+                workers=1,
+                max_hashes=1,
+            )
+            self.assertEqual(2, total)
+            self.assertEqual(
+                {b"[email protected]:hunter2", b"[email protected]:secret"},
+                set(out.read_bytes().splitlines()),
+            )
+
 
 if __name__ == "__main__":
     unittest.main()