add a pubsub database implementation

Author: Liam-DeVoe

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: minor
+
+The :doc:`Hypothesis database <database>` now supports a pub-sub interface to efficiently listen for changes in the database, via ``.add_listener`` and ``.remove_listener``. While all databases that ship with Hypothesis support this interface, implementing it is not required for custom database subclasses. Hypothesis will warn when trying to listen on a database without support.
+
+This feature is currently only used downstream in `hypofuzz <https://github.com/zac-hd/hypofuzz>`_.

hypothesis-python/setup.py

@@ -70,6 +70,7 @@ def local_file(name):
     # We also leave the choice of timezone library to the user, since it
     # might be zoneinfo or pytz depending on version and configuration.
     "django": ["django>=4.2"],
+    "watchdog": ["watchdog>=4.0.0"],
 }
 
 extras["all"] = sorted(set(sum(extras.values(), [])))