Add a dynamic declaration of spec function that does not rely on inspect

This faster function will be available once "from e3.anod.loader import
spec" statements are removed. Keep the former version for backward
compatibility.

src/e3/anod/loader.py

@@ -141,7 +141,12 @@ def __init__(
 
         # Declare spec prolog
         prolog_file = os.path.join(spec_dir, "prolog.py")
-        self.prolog_dict = {"spec_config": spec_config, "__spec_repository": self}
+        self.prolog_dict = {
+            "spec_config": spec_config,
+            "__spec_repository": self,
+            "spec": self.load,
+        }
+
         if os.path.exists(prolog_file):
             with open(prolog_file) as f:
                 exec(compile(f.read(), prolog_file, "exec"), self.prolog_dict)
@@ -271,6 +276,9 @@ def load(self, repository: AnodSpecRepository) -> Callable[..., Anod]:
 def spec(name: str) -> Callable[..., Anod]:
     """Load an Anod spec class.
 
+    Obsolete: keep until all from e3.anod.loader import spec are removed from the
+    specs.
+
     Note that two spec having the same name cannot be loaded in the same
     process as e3 keeps a cache of loaded spec using the spec basename as a
     key.