refactor: derive __version__ from package metadata (single source)

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

src/aioproxies/__init__.py

@@ -1,4 +1,6 @@
 """aioproxies - proxy parsing, formatting, and source management. see README for usage."""
+from importlib.metadata import version, PackageNotFoundError
+
 from .manager import AioProxies, ProxiesExhaustedError, ProxyManager, aioproxies
 from .proxy import Proxy, canonical_key, parse, to_proxy
 
@@ -13,4 +15,7 @@ __all__ = [
     "to_proxy",
 ]
 
-__version__ = "0.3.2"
+try:
+    __version__ = version("aioproxies")
+except PackageNotFoundError:
+    __version__ = "0.0.0+unknown"