refactor: replace eval_nix/build_nix with machine.select()

- Remove nix(), eval_nix(), and build_nix() methods from Machine class
- Add select() method that handles machine-specific attribute prefixes
- Update all usages to use machine.select() directly
- Handle Path conversion and tmp_store logic at call sites
- This simplifies the Machine API and prepares for deployment.json removal

pkgs/clan-cli/clan_lib/backups/create.py

@@ -4,7 +4,7 @@ from clan_lib.machines.machines import Machine
 
 def create_backup(machine: Machine, provider: str | None = None) -> None:
     machine.info(f"creating backup for {machine.name}")
-    backup_scripts = machine.eval_nix("config.clan.core.backups")
+    backup_scripts = machine.select("config.clan.core.backups")
     host = machine.target_host()
     if provider is None:
         if not backup_scripts["providers"]:

pkgs/clan-cli/clan_lib/backups/list.py

@@ -15,7 +15,7 @@ class Backup:
 
 def list_provider(machine: Machine, host: Remote, provider: str) -> list[Backup]:
     results = []
-    backup_metadata = machine.eval_nix("config.clan.core.backups")
+    backup_metadata = machine.select("config.clan.core.backups")
     list_command = backup_metadata["providers"][provider]["list"]
     proc = host.run(
         [list_command],
@@ -41,7 +41,7 @@ def list_provider(machine: Machine, host: Remote, provider: str) -> list[Backup]
 
 
 def list_backups(machine: Machine, provider: str | None = None) -> list[Backup]:
-    backup_metadata = machine.eval_nix("config.clan.core.backups")
+    backup_metadata = machine.select("config.clan.core.backups")
     results = []
     with machine.target_host().ssh_control_master() as host:
         if provider is None:

pkgs/clan-cli/clan_lib/backups/restore.py

@@ -7,8 +7,8 @@ from clan_lib.ssh.remote import Remote
 def restore_service(
     machine: Machine, host: Remote, name: str, provider: str, service: str
 ) -> None:
-    backup_metadata = machine.eval_nix("config.clan.core.backups")
-    backup_folders = machine.eval_nix("config.clan.core.state")
+    backup_metadata = machine.select("config.clan.core.backups")
+    backup_folders = machine.select("config.clan.core.state")
 
     if service not in backup_folders:
         msg = f"Service {service} not found in configuration. Available services are: {', '.join(backup_folders.keys())}"
@@ -60,7 +60,7 @@ def restore_backup(
     errors = []
     with machine.target_host().ssh_control_master() as host:
         if service is None:
-            backup_folders = machine.eval_nix("config.clan.core.state")
+            backup_folders = machine.select("config.clan.core.state")
             for _service in backup_folders:
                 try:
                     restore_service(machine, host, name, provider, _service)