core: allow legacy modules to be used in 'hpi module install' for backwards compatibility

but show warning

kinda hacky, but hopefully we will simplify it further when we have more such legacy modules

my/core/__main__.py

@@ -339,6 +339,9 @@ def _requires(modules: Sequence[str]) -> Sequence[str]:
     mods = [module_by_name(module) for module in modules]
     res = []
     for mod in mods:
+        if mod.legacy is not None:
+            warning(mod.legacy)
+
         reqs = mod.requires
         if reqs is None:
             error(f"Module {mod.name} has no REQUIRES specification")