feature: add apple silicon native macOS support (#81)

* feature: add apple silicon native macOS support - #81

* (macos): Fix crash

This fixes a crash when viewing the rear camera

* fix(macos): keep interpolated presentation on main thread

* fix(macos): supply Retro-WFC payload during setup

* perf(windows): compile out flat-memory fallback check

* remove duplicate smoke test

* test(macos): name and focus host platform tests

* fix(macos): validate Retro-WFC payload cache

* fix(payload): preserve staged file access failures

* Limit flat-page checks to variable-page hosts

---------

Co-authored-by: patchzyy <64382339+patchzyy@users.noreply.github.com>

runtime/tests/macos_context_abi_tests.cpp

@@ -0,0 +1,46 @@
+#include <array>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <vector>
+
+extern "C" void mkw_co_switch(void** targetSp, void** sourceSp);
+extern "C" void* mkw_co_init(void* stackTop, void (*entry)(void*), void* argument);
+
+namespace {
+// Exercise the raw AArch64 context ABI independently of HostContext so a
+// callee-saved-register or stack-frame regression is localized to this layer.
+
+std::array<std::byte, 64 * 1024> g_workerStack{};
+void* g_schedulerSp = nullptr;
+void* g_workerSp = nullptr;
+std::vector<int> g_events;
+
+void Worker(void*) {
+    g_events.push_back(1);
+    mkw_co_switch(&g_schedulerSp, &g_workerSp);
+    g_events.push_back(2);
+    mkw_co_switch(&g_schedulerSp, &g_workerSp);
+    std::abort();
+}
+
+} // namespace
+
+int main() {
+    g_workerSp = mkw_co_init(g_workerStack.data() + g_workerStack.size(), Worker, nullptr);
+    if (!g_workerSp) {
+        std::cerr << "failed to create AArch64 context frame\n";
+        return 1;
+    }
+    mkw_co_switch(&g_workerSp, &g_schedulerSp);
+    if (g_events != std::vector<int>{1}) {
+        std::cerr << "worker did not yield to scheduler\n";
+        return 1;
+    }
+    mkw_co_switch(&g_workerSp, &g_schedulerSp);
+    if (g_events != std::vector<int>{1, 2}) {
+        std::cerr << "worker did not resume from saved context\n";
+        return 1;
+    }
+    return 0;
+}