systemd: Add support for managing cgroups through systemd

`SystemdCgroup` takes a `parent`, which is the name of a slice, and a
`unit`, which is the name of a slice or a scope unit, and provides methods
to start, kill the unit, as well as set properties for the unit.

The mods, `cpu`, `memory`, `cpuset`, and `pids`, are designed to generate
properties quickly. It hides the difference between cgroups v1 and v2, and
does simple checks for the systemd version and arguments.

Signed-off-by: Xuewei Niu <niuxuewei.nxw@antgroup.com>

src/systemd/dbus/proxy.rs

@@ -0,0 +1,16 @@
+// Copyright (c) 2025 Ant Group
+//
+// SPDX-License-Identifier: Apache-2.0 or MIT
+//
+
+use zbus::blocking::Connection;
+use zbus::Result;
+
+use crate::systemd::dbus::systemd_manager_proxy::ManagerProxyBlocking as SystemManager;
+
+pub(crate) fn systemd_manager_proxy<'a>() -> Result<SystemManager<'a>> {
+    let connection = Connection::system()?;
+    let proxy = SystemManager::new(&connection)?;
+
+    Ok(proxy)
+}