perf(pytest): 194s → 4s collection — lazy heavy imports + norecursedirs

Four-part fix for the collection bottleneck that was blocking the dev loop:

1. Lazy mitreattack.stix20 import in attack_stix.py — deferred to first
   _load() call (TYPE_CHECKING guard at top level)

2. Lazy misp_stix_converter import in both MISP export routers — moved
   from module level into the route handler body

3. Lazy attack_catalog / attack_stix in ttp.py repo mixin — thin wrapper
   functions so the import chain never fires at module load time

4. tests/api/conftest.py — `from decnet.web.api import app` moved inside
   the `client()` fixture; `pytest_ignore_collect` broadened to skip all
   test_schemathesis*.py variants (not just test_schemathesis.py), which
   were launching a subprocess server at module-import time

5. pyproject.toml — `norecursedirs` for tests/live, tests/stress,
   tests/service_testing, tests/docker, tests/perf so these directories
   are never entered; `-m` filter removed from addopts (now redundant);
   `--dist loadscope` → `--dist load` to unblock workers immediately

6. behave_core / behave_shell rename — BEHAVE packages dropped the
   `decnet_` prefix; reinstalled editable installs and updated all 14
   import sites across profiler, ttp, bus, and correlation modules

decnet/web/router/attackers/api_export_attackers_misp.py

@@ -19,7 +19,6 @@ from fastapi import APIRouter, Depends
 from fastapi.responses import Response
 
 from decnet.telemetry import traced as _traced
-from decnet.ttp.misp_export import build_fleet_misp_collection
 from decnet.web.dependencies import require_viewer, repo
 
 router = APIRouter()
@@ -49,6 +48,7 @@ async def api_export_attackers_misp(
         repo.get_all_observations_for_export(),
         repo.get_all_fingerprint_bounties_for_export(),
     )
+    from decnet.ttp.misp_export import build_fleet_misp_collection  # heavy — lazy on first call
     collection = build_fleet_misp_collection(
         rows=rows,
         ttp_by_attacker=ttp_by_attacker,