refactor: derive __version__ from package metadata (single source)

Signed-off-by: disqualifier <dev@disqualifier.me>

src/dpy_webhooks/__init__.py

@@ -2,6 +2,8 @@
 
 see :mod:`dpy_webhooks.dpy_webhooks` for the full module docstring, api, and error contract
 """
+from importlib.metadata import PackageNotFoundError, version
+
 from .dpy_webhooks import (
     MAX_WEBHOOKS_PER_CHANNEL,
     PICK_STRATEGIES,
@@ -12,7 +14,10 @@ from .dpy_webhooks import (
     WebhookStore,
 )
 
-__version__ = "0.1.1"
+try:
+    __version__ = version("dpy_webhooks")
+except PackageNotFoundError:
+    __version__ = "0.0.0+unknown"
 
 __all__ = [
     "DPYWebhooks",