fix(server): honour the legacy thresholds: config; repair the stale test suite

Since the built-in defaults were seeded into threshold_configs, the legacy
top-level thresholds: format was silently ignored. get_thresholds_for_host
now uses it whenever it was configured.

Tests: point imports at hbd.server/hbd.common, rewrite the DNS worker,
proto, datagram and threshold tests for the current API, add pytest-asyncio
to the dev extras and set testpaths so a bare pytest runs cleanly.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/test_proto.py

@@ -1,19 +1,19 @@
-from hbd.proto import dicttos, stodict, oldmtodict
+from hbd.common.proto import dicttos, stodict, oldmtodict
 
 
-def test_dicttos_and_stodict_uncompressed():
+def test_dicttos_and_stodict_roundtrip():
     msg = dicttos("HTB", {"name": "host.example", "interval": 10})
+    assert msg.startswith(b"!HTB:")
     d = stodict(msg)
-    assert d["ID"].startswith("HTB")
+    assert d["ID"] == "HTB"
     assert d["name"] == "host.example"
     assert d["interval"] == 10
 
 
-def test_dicttos_and_stodict_compressed():
-    msg = dicttos("ACK", {"time": 12345}, compress=True)
-    d = stodict(msg)
-    # for compressed the original code included the colon in ID slice; ensure no crash
-    assert "ID" in d
+def test_dicttos_and_stodict_ack():
+    d = stodict(dicttos("ACK", {"time": 12345}))
+    assert d["ID"] == "ACK"
+    assert d["time"] == 12345
 
 
 def test_oldmtodict():