vars: retrieve generators for multiple machines

This is necessary ground work for fixing regeneration behavior spanning over multiple machines

pkgs/clan-cli/clan_lib/flash/flash.py

@@ -118,7 +118,9 @@ def run_machine_flash(
 
         from clan_cli.vars.generator import Generator
 
-        for generator in Generator.get_machine_generators(machine.name, machine.flake):
+        for generator in Generator.get_machine_generators(
+            [machine.name], machine.flake
+        ):
             for file in generator.files:
                 if file.needed_for == "partitioning":
                     msg = f"Partitioning time secrets are not supported with `clan flash write`: clan.core.vars.generators.{generator.name}.files.{file.name}"