feat: expose function for provider->version map (#136)

Signed-off-by: Weston Steimel <[email protected]>

src/vunnel/providers/__init__.py

@@ -26,7 +26,7 @@
 if TYPE_CHECKING:
     from vunnel import provider
 
-_providers = {
+_providers: dict[str, type[provider.Provider]] = {
     alpine.Provider.name(): alpine.Provider,
     amazon.Provider.name(): amazon.Provider,
     centos.Provider.name(): centos.Provider,
@@ -49,6 +49,10 @@ def names() -> list[str]:
     return sorted(_providers.keys())
 
 
+def versions() -> dict[str, int]:
+    return {n: p.version() for (n, p) in _providers.items()}
+
+
 def register(name: str, cls: type[provider.Provider]) -> None:
     if name in _providers and _providers[name] != cls:
         raise KeyError(f"provider {name!r} is already registered to another provider class: {_providers[name]!r}")