feat(image): add icns support (#2120)

## Description

Add support for icns using sips

## Screenshots

<img width="708" height="910" alt="image"
src="https://github.com/user-attachments/assets/9ca85b23-e020-4b05-9aeb-6d40666d71b6"
/>

Co-authored-by: Folke Lemaitre <folke.lemaitre@gmail.com>

lua/snacks/image/convert.lua

@@ -47,6 +47,15 @@ local uv = vim.uv or vim.loop
 
 ---@type table<string, snacks.image.cmd>
 local commands = {
+  icns = {
+    ft = "png",
+    cmd = {
+      {
+        cmd = "sips",
+        args = { "-s", "format", "png", "{src}", "--out", "{file}" },
+      },
+    },
+  },
   url = {
     cmd = {
       {

lua/snacks/image/init.lua

@@ -64,6 +64,7 @@ local defaults = {
     "mkv",
     "webm",
     "pdf",
+    "icns",
   },
   force = false, -- try displaying the image, even if the terminal does not support it
   doc = {

lua/snacks/init.lua

@@ -38,6 +38,7 @@ local config = {
       "mkv",
       "webm",
       "pdf",
+      "icns",
     },
   },
 }