feat(pkg): opencv module package on macOS (import opencv.cv)

The public `opencv` C++23-module package (pkgs/o/opencv.lua) now offers macosx —
the v0.0.4 module tarball is OS-neutral (module source), and its compat.opencv
dependency is macOS-capable (linux+macosx full profile, PR#97). So mcpp-ecosystem
macOS users get `import opencv.cv;` (core/imgproc/imgcodecs/highgui/videoio+FFmpeg)
with the same simple `opencv = "0.0.4"` dependency as linux — no new module release.

- pkgs/o/opencv.lua: +xpm.macosx (same tarball/sha as linux).
- members opencv-module + opencv-module-unifont -> +cfg(macos); test guards
  __linux__ -> __linux__||__APPLE__. opencv-module-dnn stays linux (dnn = x86 SIMD
  kernels + protobuf/mlas; needs a macOS dnn snapshot). windows not offered for the
  module yet (import opencv.cv aggregates videoio; windows compat.opencv is core-only).

Author: Sunrisepeak

pkgs/o/opencv.lua

@@ -10,7 +10,9 @@
 -- Optional features (0.0.4+, mcpp#243 forwarding): `dnn` adds the
 -- import opencv.dnn; interface and forwards compat.opencv/dnn; `unifont`
 -- forwards compat.opencv/unifont — `opencv = { features = ["dnn"] }`.
--- Linux-only for now: compat.opencv carries a linux-x86_64 config snapshot.
+-- linux + macOS: compat.opencv carries per-OS config snapshots (linux-x86_64,
+    -- macosx-arm64 full profiles). windows is core-only (no videoio) so the module
+    -- (import opencv.cv aggregates videoio) is not yet offered there.
 --
 package = {
     spec        = "1",
@@ -31,6 +33,15 @@ package = {
                 sha256 = "a2e95e8b22ae66712e3f78809426e058330073c2679a21c2b2d500faa0b4964f",
             },
         },
+        macosx = {
+            ["0.0.4"] = {
+                url    = {
+                    GLOBAL = "https://github.com/Sunrisepeak/opencv-m/archive/refs/tags/v0.0.4.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/opencv/releases/download/v0.0.4/opencv-m-0.0.4.tar.gz",
+                },
+                sha256 = "a2e95e8b22ae66712e3f78809426e058330073c2679a21c2b2d500faa0b4964f",
+            },
+        },
     },
 
     -- (no `mcpp` field -- default lookup will find <verdir>/*/mcpp.toml)

tests/examples/opencv-module-unifont/mcpp.toml

@@ -12,3 +12,6 @@ default = { path = "../../.." }
 
 [target.'cfg(linux)'.dependencies]
 opencv = { version = "0.0.4", features = ["unifont"] }
+
+[target.'cfg(macos)'.dependencies]
+opencv = { version = "0.0.4", features = ["unifont"] }

tests/examples/opencv-module-unifont/tests/opencv_unifont_iface.cpp

@@ -2,7 +2,7 @@
 // compat.opencv/unifont — CJK rendering through the module layer must ink.
 // Linux-only (see mcpp.toml). Import-only (import std + opencv.cv): no textual
 // headers, matching the ffmpeg-module member convention.
-#ifdef __linux__
+#if defined(__linux__) || defined(__APPLE__)
 import std;
 import opencv.cv;
 

tests/examples/opencv-module/mcpp.toml

@@ -18,3 +18,6 @@ default = { path = "../../.." }
 
 [target.'cfg(linux)'.dependencies]
 opencv = "0.0.4"
+
+[target.'cfg(macos)'.dependencies]
+opencv = "0.0.4"

tests/examples/opencv-module/tests/opencv_module.cpp

@@ -3,7 +3,7 @@
 // replacement operator surface: Size comparison via != crosses the module
 // boundary — the v0.0.1 regression scenario), PNG+JPEG codec roundtrips,
 // videoio registry. Linux-only (see mcpp.toml).
-#ifdef __linux__
+#if defined(__linux__) || defined(__APPLE__)
 import std;
 import opencv.cv;