rename nix_shell_legacy to nix_shell and run_cmd to nix_shell

Than it's more obvious that we need to migrate.

pkgs/clan-cli/clan_cli/facts/generate.py

@@ -18,7 +18,7 @@ from clan_cli.errors import ClanError
 from clan_cli.git import commit_files
 from clan_cli.machines.inventory import get_all_machines, get_selected_machines
 from clan_cli.machines.machines import Machine
-from clan_cli.nix import nix_shell
+from clan_cli.nix import nix_shell_legacy
 
 from .check import check_secrets
 from .public_modules import FactStoreBase
@@ -39,7 +39,7 @@ def read_multiline_input(prompt: str = "Finish with Ctrl-D") -> str:
 
 def bubblewrap_cmd(generator: str, facts_dir: Path, secrets_dir: Path) -> list[str]:
     # fmt: off
-    return nix_shell(
+    return nix_shell_legacy(
         [
             "nixpkgs#bash",
             "nixpkgs#bubblewrap",