Replace go-spew + go-difflib with go-cmp

[mtrmac]

github.com/davecgh/go-spew and github.com/pmezard/go-difflib both have last commits 8 years ago; go-difflib is explicitly unmaintained. Instead, use github.com/google/go-cmp, which seems at least minimally maintained.

This is locally motivated by stretrchr/testify no longer depending on the 2 packages (... by copying them into the testify package...).

Note that all three of go-spew / go-difflib / go-cmp are, except for this one call, used only in tests (the 2 previously in stretrchr/testify, go-spew in onsi/gomega).

The go-spew implementation is a bit heavier than we might like, but the code is only used for debug logs, and worrying less about our supply chains seems valuable.

Previous output (from tests in this package):

time="2026-08-17T20:29:50+02:00" level=error msg="precreate hook 0 made configuration changes:\n--- Old\n+++ New\n@@ -19,3 +19,3 @@\n   Namespaces: ([]specs.LinuxNamespace) <nil>,\n-  Devices: ([]specs.LinuxDevice) (len=1) {\n+  Devices: ([]specs.LinuxDevice) (len=2) {\n    (specs.LinuxDevice) {\n@@ -25,2 +25,11 @@\n     Minor: (int64) 229,\n+    FileMode: (*fs.FileMode)(-rw-------),\n+    UID: (*uint32)(0),\n+    GID: (*uint32)(0)\n+   },\n+   (specs.LinuxDevice) {\n+    Path: (string) (len=8) \"/dev/sda\",\n+    Type: (string) (len=1) \"b\",\n+    Major: (int64) 8,\n+    Minor: (int64) 0,\n     FileMode: (*fs.FileMode)(-rw-------),\n"
time="2026-08-17T20:29:50+02:00" level=error msg="precreate hook 1 made configuration changes:\n--- Old\n+++ New\n@@ -30,3 +30,3 @@\n    (specs.LinuxDevice) {\n-    Path: (string) (len=8) \"/dev/sda\",\n+    Path: (string) (len=8) \"/dev/sdb\",\n     Type: (string) (len=1) \"b\",\n"

(Yes we are logging the diff at a single line)

maps to:

precreate hook 0 made configuration changes:
--- Old
+++ New
@@ -19,3 +19,3 @@
   Namespaces: ([]specs.LinuxNamespace) <nil>,
-  Devices: ([]specs.LinuxDevice) (len=1) {
+  Devices: ([]specs.LinuxDevice) (len=2) {
    (specs.LinuxDevice) {
@@ -25,2 +25,11 @@
     Minor: (int64) 229,
+    FileMode: (*fs.FileMode)(-rw-------),
+    UID: (*uint32)(0),
+    GID: (*uint32)(0)
+   },
+   (specs.LinuxDevice) {
+    Path: (string) (len=8) "/dev/sda",
+    Type: (string) (len=1) "b",
+    Major: (int64) 8,
+    Minor: (int64) 0,
     FileMode: (*fs.FileMode)(-rw-------),

precreate hook 1 made configuration changes:
--- Old
+++ New
@@ -30,3 +30,3 @@
    (specs.LinuxDevice) {
-    Path: (string) (len=8) "/dev/sda",
+    Path: (string) (len=8) "/dev/sdb",
     Type: (string) (len=1) "b",

New output:

time="2026-08-17T20:37:11+02:00" level=error msg="precreate hook 0 made configuration changes:\n\u00a0\u00a0&specs.Spec{\n\u00a0\u00a0\t... // 6 identical fields\n\u00a0\u00a0\tHooks:       nil,\n\u00a0\u00a0\tAnnotations: nil,\n\u00a0\u00a0\tLinux: &specs.Linux{\n\u00a0\u00a0\t\t... // 4 identical fields\n\u00a0\u00a0\t\tCgroupsPath: \"\",\n\u00a0\u00a0\t\tNamespaces:  nil,\n\u00a0\u00a0\t\tDevices: []specs.LinuxDevice{\n\u00a0\u00a0\t\t\t{Path: \"/dev/fuse\", Type: \"c\", Major: 10, Minor: 229, ...},\n+\u00a0\t\t\t{Path: \"/dev/sda\", Type: \"b\", Major: 8, FileMode: s\"-rw-------\", UID: &0, GID: &0},\n\u00a0\u00a0\t\t},\n\u00a0\u00a0\t\tNetDevices: nil,\n\u00a0\u00a0\t\tSeccomp:    nil,\n\u00a0\u00a0\t\t... // 8 identical fields\n\u00a0\u00a0\t},\n\u00a0\u00a0\tSolaris: nil,\n\u00a0\u00a0\tWindows: nil,\n\u00a0\u00a0\t... // 3 identical fields\n\u00a0\u00a0}\n"
time="2026-08-17T20:37:11+02:00" level=error msg="precreate hook 1 made configuration changes:\n\u00a0\u00a0&specs.Spec{\n\u00a0\u00a0\t... // 6 identical fields\n\u00a0\u00a0\tHooks:       nil,\n\u00a0\u00a0\tAnnotations: nil,\n\u00a0\u00a0\tLinux: &specs.Linux{\n\u00a0\u00a0\t\t... // 4 identical fields\n\u00a0\u00a0\t\tCgroupsPath: \"\",\n\u00a0\u00a0\t\tNamespaces:  nil,\n\u00a0\u00a0\t\tDevices: []specs.LinuxDevice{\n\u00a0\u00a0\t\t\t{Path: \"/dev/fuse\", Type: \"c\", Major: 10, Minor: 229, ...},\n\u00a0\u00a0\t\t\t{\n-\u00a0\t\t\t\tPath:  \"/dev/sda\",\n+\u00a0\t\t\t\tPath:  \"/dev/sdb\",\n\u00a0\u00a0\t\t\t\tType:  \"b\",\n\u00a0\u00a0\t\t\t\tMajor: 8,\n\u00a0\u00a0\t\t\t\t... // 4 identical fields\n\u00a0\u00a0\t\t\t},\n\u00a0\u00a0\t\t},\n\u00a0\u00a0\t\tNetDevices: nil,\n\u00a0\u00a0\t\tSeccomp:    nil,\n\u00a0\u00a0\t\t... // 8 identical fields\n\u00a0\u00a0\t},\n\u00a0\u00a0\tSolaris: nil,\n\u00a0\u00a0\tWindows: nil,\n\u00a0\u00a0\t... // 3 identical fields\n\u00a0\u00a0}\n"

maps to:

precreate hook 0 made configuration changes:
  &specs.Spec{
      ... // 6 identical fields
      Hooks:       nil,
      Annotations: nil,
      Linux: &specs.Linux{
              ... // 4 identical fields
              CgroupsPath: "",
              Namespaces:  nil,
              Devices: []specs.LinuxDevice{
                      {Path: "/dev/fuse", Type: "c", Major: 10, Minor: 229, ...},
+                      {Path: "/dev/sda", Type: "b", Major: 8, FileMode: s"-rw-------", UID: &0, GID: &0},
              },
              NetDevices: nil,
              Seccomp:    nil,
              ... // 8 identical fields
      },
      Solaris: nil,
      Windows: nil,
      ... // 3 identical fields
  }

precreate hook 1 made configuration changes:
  &specs.Spec{
      ... // 6 identical fields
      Hooks:       nil,
      Annotations: nil,
      Linux: &specs.Linux{
              ... // 4 identical fields
              CgroupsPath: "",
              Namespaces:  nil,
              Devices: []specs.LinuxDevice{
                      {Path: "/dev/fuse", Type: "c", Major: 10, Minor: 229, ...},
                      {
-                              Path:  "/dev/sda",
+                              Path:  "/dev/sdb",
                              Type:  "b",
                              Major: 8,
                              ... // 4 identical fields
                      },
              },
              NetDevices: nil,
              Seccomp:    nil,
              ... // 8 identical fields
      },
      Solaris: nil,
      Windows: nil,
      ... // 3 identical fields
  }

is a bit more chatty, *shrug*.