Add aeg.cipher(alg) for loading modules by name in str. Added aeg.CIPHERS mapping of the nominal names to module names and Cipher for typing literals.

src/aeg/__init__.py

@@ -0,0 +1,16 @@
+import importlib
+
+from ._ciphers import CIPHERS, CipherName
+from ._typing import Cipher
+
+__all__ = ["cipher", "CIPHERS", "Cipher", "CipherName"]
+
+
+def cipher(alg: CipherName) -> Cipher:
+    """Acquire a cipher module by name."""
+    name = alg.lower().replace("-", "")
+    if name == "aegis128":
+        name = "aegis128l"  # AEGIS-128 is dead, the user meant AEGIS-128L
+    if name in CIPHERS.values():
+        return importlib.import_module(f".{name}", __package__)  # type: ignore[return-value]
+    raise ValueError(f"Unknown algorithm {alg!r}. Valid options: {', '.join(CIPHERS)}")