refactor: remove Machine.vars_generators() method

Replace all calls to machine.vars_generators() with direct calls to
Generator.generators_from_flake() to make the dependency more explicit
and remove unnecessary indirection.

This reduces coupling to the Machine class, making the codebase more
modular and easier to refactor in the future.

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

@@ -187,7 +187,10 @@ def decrypt_dependencies(
     decrypted_dependencies: dict[str, Any] = {}
     for generator_name in set(generator.dependencies):
         decrypted_dependencies[generator_name] = {}
-        for dep_generator in machine.vars_generators():
+        generators = Generator.generators_from_flake(
+            machine.name, machine.flake, machine
+        )
+        for dep_generator in generators:
             if generator_name == dep_generator.name:
                 break
         else:
@@ -395,7 +398,9 @@ def get_closure(
 ) -> list[Generator]:
     from . import graph
 
-    vars_generators = machine.vars_generators()
+    vars_generators = Generator.generators_from_flake(
+        machine.name, machine.flake, machine
+    )
     generators: dict[str, Generator] = {
         generator.name: generator for generator in vars_generators
     }
@@ -470,7 +475,11 @@ def generate_vars_for_machine(
 
     machine = Machine(name=machine_name, flake=Flake(str(base_dir)))
     generators_set = set(generators)
-    generators_ = [g for g in machine.vars_generators() if g.name in generators_set]
+    generators_ = [
+        g
+        for g in Generator.generators_from_flake(machine_name, machine.flake, machine)
+        if g.name in generators_set
+    ]
 
     return _generate_vars_for_machine(
         machine=machine,
@@ -489,7 +498,10 @@ def generate_vars_for_machine_interactive(
 ) -> bool:
     _generator = None
     if generator_name:
-        for generator in machine.vars_generators():
+        generators = Generator.generators_from_flake(
+            machine.name, machine.flake, machine
+        )
+        for generator in generators:
             if generator.name == generator_name:
                 _generator = generator
                 break