refactor(intel): migrate AttackerIntel JSON-string columns to native SQLAlchemy JSON

Five list columns (greynoise_tags, abuseipdb_categories, threatfox_threat_types,
threatfox_ioc_types, threatfox_malware_families) and four dict columns
(*_raw) are now Column(JSON) with list/dict type annotations and
default_factory=list/dict. Providers return native Python objects; the
application-layer json.dumps/json.loads round-trip and _decode_json_list
helpers are gone. to_intel_event_payload() reads columns directly.

Also caps pytest xdist at -n 4 and excludes tests/api from norecursedirs
to prevent schemathesis workers from OOM-killing the dev loop.

decnet/intel/abuseipdb.py

@@ -17,7 +17,6 @@ later if operators report drift.
 """
 from __future__ import annotations
 
-import json
 import os
 from datetime import datetime, timezone
 from typing import Optional
@@ -110,8 +109,8 @@ class AbuseIPDBProvider(IntelProvider):
             verdict=verdict,
             column_updates={
                 "abuseipdb_score": score,
-                "abuseipdb_categories": json.dumps(sorted(categories)),
-                "abuseipdb_raw": json.dumps(data),
+                "abuseipdb_categories": sorted(categories),
+                "abuseipdb_raw": data,
                 "abuseipdb_queried_at": datetime.now(timezone.utc),
             },
         )