[FIX] significantly speed up local testing

The mergebot tests have always been pretty gentle on system load which
is nice, however it's just looking at the list of longest tests that I
realised / re-membered the hook wait duration is 10 seconds for the
benefit of github, which doesn't really matter locally. This means on
interaction / cron-heavy tests the test might only be using on the
order of 10% CPU or something, that is a waste of time.

TBF this is easily compensated by increasing the concurrency of the
test suite (e.g. from 16 to 32 when I switched machine, but it seems
as if not more sensible to lower the webhook wait delay to something
more reasonable. 1s seems to be a good fit here, on my new computer at
n=16 it leads to the test suite running in 15mn at 600% CPU (which is
pretty good on a 6/12 CPU as it loads the system heavily but doesn't
completely bog it down).

Reducing it to 0.5s, the test suite takes the same duration but CPU
load increases to 770%, and errors creep up, likely a mix of
concurrency issues in the DB and dummy-central sending webhooks too
slowly as we compete with it for CPU resources (could actually make
sense to restrict the number of threads tokio can use). Reducing
concurrency could make this work better, but I think at this point
we're in a pretty good state, it's even somewhat reasonable to run the
test suite sequentially (taking about 1h10 but being functionally
invisible in terms of load).

conftest.py

@@ -78,6 +78,18 @@ import requests
 NGROK_CLI = [
     'ngrok', 'start', '--none', '--region', 'eu',
 ]
+# When an operation can trigger webhooks, the test suite has to wait *some time*
+# in the hope that the webhook(s) will have been dispatched by the end as github
+# provides no real webhook feedback (e.g. an event stream).
+#
+# This also acts as a bit of a rate limiter, as github has gotten more and more
+# angry with that. Especially around event-generating limits.
+#
+# TODO: explore https://docs.github.com/en/rest/using-the-rest-api/rate-limits-for-the-rest-api
+#       and see if it would be possible to be a better citizen (e.g. add test
+#       retry / backoff using GH tighter GH integration)
+WEBHOOK_WAIT_TIME = 10  # seconds
+LOCAL_WEBHOOK_WAIT_TIME = 1
 
 def pytest_addoption(parser):
     parser.addoption('--addons-path')
@@ -98,7 +110,12 @@ def pytest_addoption(parser):
 def is_manager(config):
     return not hasattr(config, 'workerinput')
 
-def pytest_configure(config):
+def pytest_configure(config: pytest.Config) -> None:
+    global WEBHOOK_WAIT_TIME
+    # no tunnel => local setup, no need to wait as much
+    if not config.getoption('--tunnel'):
+        WEBHOOK_WAIT_TIME = LOCAL_WEBHOOK_WAIT_TIME
+
     sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'mergebot_test_utils'))
     config.addinivalue_line(
         "markers",
@@ -109,7 +126,6 @@ def pytest_configure(config):
         "defaultstatuses: use the statuses `default` rather than `ci/runbot,legal/cla`",
     )
 
-
 def pytest_unconfigure(config):
     if not is_manager(config):
         return
@@ -126,7 +142,7 @@ def _set_socket_timeout():
     socket.setdefaulttimeout(120.0)
 
 @pytest.fixture(scope="session")
-def config(pytestconfig):
+def config(pytestconfig: pytest.Config) -> dict[str, dict[str, str]]:
     """ Flat version of the pytest config file (pytest.ini), parses to a
     simple dict of {section: {key: value}}
 
@@ -211,7 +227,7 @@ def users(partners, rolemap):
     return {k: v['login'] for k, v in rolemap.items()}
 
 @pytest.fixture(scope='session')
-def tunnel(pytestconfig, port):
+def tunnel(pytestconfig: pytest.Config, port: int):
     """ Creates a tunnel to localhost:<port> using ngrok or localtunnel, should yield the
     publicly routable address & terminate the process at the end of the session
     """
@@ -368,8 +384,8 @@ def db(request, module, dbcache, tmpdir):
     if not request.config.getoption('--no-delete'):
         subprocess.run(['dropdb', rundb], check=True)
 
-def wait_for_hook(n=1):
+def wait_for_hook():
-    time.sleep(10 * n)
+    time.sleep(WEBHOOK_WAIT_TIME)
 
 def wait_for_server(db, port, proc, mod, timeout=120):
     """ Polls for server to be response & have installed our module.
@@ -999,11 +1015,11 @@ class Repo:
                 return
 
     def __enter__(self):
-        self.hook = 1
+        self.hook = True
         return self
     def __exit__(self, *args):
-        wait_for_hook(self.hook)
+        wait_for_hook()
-        self.hook = 0
+        self.hook = False
     class Commit:
         def __init__(self, message, *, author=None, committer=None, tree, reset=False):
             self.id = None
@@ -1137,7 +1153,6 @@ class PR:
             headers=headers
         )
         assert 200 <= r.status_code < 300, r.text
-        wait_for_hook()
 
     def delete_comment(self, cid, token=None):
         assert self.repo.hook