refactor: derive __version__ from package metadata (single source)

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

src/dpy_paginator/__init__.py

@@ -1,3 +1,10 @@
+from importlib.metadata import version, PackageNotFoundError
+
 from .dpy_paginator import DPYPaginator, ButtonPaginator, JumpToPageModal, DEFAULT_EMOJIS, Page
 
-__all__ = ["DPYPaginator", "ButtonPaginator", "JumpToPageModal", "DEFAULT_EMOJIS", "Page"]
+try:
+    __version__ = version("dpy_paginator")
+except PackageNotFoundError:
+    __version__ = "0.0.0+unknown"
+
+__all__ = ["DPYPaginator", "ButtonPaginator", "JumpToPageModal", "DEFAULT_EMOJIS", "Page", "__version__"]