feat(agent): system info collector for pveversion/zfs/apt

agent/test/fixtures/system/apt_upgradable.txt

@@ -0,0 +1,3 @@
+Listing...
+libssl3/stable 3.0.11-1~deb12u2 amd64 [upgradable from: 3.0.11-1~deb12u1]
+openssh-server/stable 1:9.2p1-2+deb12u3 amd64 [upgradable from: 1:9.2p1-2+deb12u2]

agent/test/fixtures/system/pveversion.txt

@@ -0,0 +1 @@
+pve-manager/8.3.1/abc123 (running kernel: 6.8.12-1-pve)

agent/test/fixtures/system/zfs_version.txt

@@ -0,0 +1,2 @@
+zfs-2.3.0-pve2
+zfs-kmod-2.3.0-pve2

agent/test/proxmox_agent/collectors/system_info_test.exs

@@ -0,0 +1,38 @@
+defmodule ProxmoxAgent.Collectors.SystemInfoTest do
+  use ExUnit.Case, async: true
+
+  alias ProxmoxAgent.Collectors.SystemInfo
+
+  @fixtures Path.expand("../../fixtures/system", __DIR__)
+
+  defp fake_runner do
+    fn
+      "pveversion", [] -> {:ok, File.read!(Path.join(@fixtures, "pveversion.txt"))}
+      "zfs", ["--version"] -> {:ok, File.read!(Path.join(@fixtures, "zfs_version.txt"))}
+      "apt", ["list", "--upgradable"] -> {:ok, File.read!(Path.join(@fixtures, "apt_upgradable.txt"))}
+    end
+  end
+
+  test "collects pveversion, zfs version and pending upgrade count" do
+    sample = SystemInfo.collect(runner: fake_runner())
+
+    assert sample.pve_version =~ "pve-manager/8.3.1"
+    assert sample.zfs_version =~ "2.3.0"
+    assert sample.pending_updates == 2
+    assert sample.errors == []
+  end
+
+  test "partial sample when one command fails" do
+    partial = fn
+      "pveversion", [] -> {:ok, "pve-manager/8.3.1/abc (running kernel: 6.8.12-1-pve)\n"}
+      "zfs", ["--version"] -> {:error, {:enoent, "zfs"}}
+      "apt", ["list", "--upgradable"] -> {:ok, "Listing...\n"}
+    end
+
+    sample = SystemInfo.collect(runner: partial)
+    assert sample.pve_version =~ "8.3.1"
+    assert sample.zfs_version == nil
+    assert sample.pending_updates == 0
+    assert length(sample.errors) == 1
+  end
+end