feat: add the sghi.dispatch module

Add the `sghi.dispatch` module which contains a Multiple-producer-multiple-accept signal-dispatcher implementation heavily inspired by [PyDispatcher](https://grass.osgeo.org/grass83/manuals/libpython/pydispatch.html) and [Django dispatch](https://docs.djangoproject.com/en/dev/topics/signals/).

docs/conf.py

@@ -65,13 +65,15 @@
     ("py:class", "TracebackType"),  # Used as type annotation. Only available when type checking
     ("py:class", "concurrent.futures._base.Executor"),  # sphinx can't find it
     ("py:class", "concurrent.futures._base.Future"),  # sphinx can't find it
+    ("py:class", "sghi.dispatch._ST_contra"),  # private type annotations
     ("py:class", "sghi.task._IT"),  # private type annotations
     ("py:class", "sghi.task._OT"),  # private type annotations
     ("py:class", "sghi.utils.checkers._Comparable"),  # private type annotations
     ("py:class", "sghi.utils.checkers._ST"),  # private type annotations
     ("py:class", "sghi.utils.checkers._T"),  # private type annotations
     ("py:class", "sghi.utils.module_loading._T"),  # private type annotations
     ("py:class", "sghi.typing._CT_contra"),  # private type annotations
+    ("py:obj", "sghi.dispatch._ST_contra"),  # private type annotations
     ("py:obj", "sghi.disposable.decorators.not_disposed._P"),  # private type annotations
     ("py:obj", "sghi.disposable.decorators.not_disposed._R"),  # private type annotations
     ("py:obj", "sghi.task._IT"),  # private type annotations

docs/index.rst

@@ -42,6 +42,7 @@ API Reference
 
      sghi.app
      sghi.config
+     sghi.dispatch
      sghi.disposable
      sghi.exceptions
      sghi.task

src/sghi/app.py

@@ -18,12 +18,25 @@
 from typing import Any, Final
 
 from .config import Config, SettingInitializer
+from .dispatch import Dispatcher
 
 # =============================================================================
 # GLOBAL APPLICATION/TOOL CONSTANTS
 # =============================================================================
 
 
+dispatcher: Final[Dispatcher] = Dispatcher.of_proxy()
+"""The main application :class:`dispatcher<sghi.dispatch.Dispatcher>`.
+
+.. admonition:: Note: To application authors
+    :class: note
+
+    This value is set to an instance of :class:`sghi.dispatch.DispatcherProxy`-
+    enabling the default wrapped instance to be replaced with a more
+    appropriate value during application setup.
+
+"""
+
 conf: Final[Config] = Config.of_proxy()
 """The application configurations.