Implement ZFS dataset management and snapshot configuration

- Introduced a new `datasets.nix` file to define ZFS datasets and their properties, allowing for centralized management of dataset configurations.
- Updated `default.nix` to import and enable the `zfs_manager` service, integrating it into the system configuration.
- Refactored `zfs.sh` to remove dataset creation commands, delegating dataset management to the `zfs_manager` service.
- Removed the legacy `snapshot_config.toml` file, as snapshot configurations are now handled within `datasets.nix`.
- Modified `vars.nix` to derive mountpoint paths from `datasets.nix`, ensuring consistency across the configuration.
- Created a new `zfs.nix` file to define the `zfs_manager` service and its dependencies.
- Added comprehensive tests for the `zfs_manager` functionality, covering dataset creation, property management, and error handling.

systems/jeeves/default.nix

@@ -1,7 +1,4 @@
 { inputs, ... }:
-let
-  vars = import ./vars.nix;
-in
 {
   imports = [
     "${inputs.self}/users/dov"
@@ -15,6 +12,7 @@ in
     "${inputs.self}/common/optional/syncthing_base.nix"
     "${inputs.self}/common/optional/update.nix"
     "${inputs.self}/common/optional/zerotier.nix"
+    "${inputs.self}/common/optional/zfs_manager.nix"
     ./monitoring
     ./docker
     ./services
@@ -24,6 +22,7 @@ in
     ./programs.nix
     ./runners
     ./syncthing.nix
+    ./zfs.nix
   ];
 
   services = {
@@ -31,11 +30,6 @@ in
 
     smartd.enable = true;
 
-    snapshot_manager = {
-      path = ./snapshot_config.toml;
-      EnvironmentFile = "${vars.secrets}/services/snapshot_manager";
-    };
-
     zerotierone.joinNetworks = [ "a09acf02330d37b9" ];
   };