LOC-7291: download darwin-arm64 binary on Apple Silicon

On macOS the binding now selects BrowserStackLocal-darwin-arm64 when
the runtime reports arm64 (same runtime-arch detection the linux-arm64
path already uses); x64 runtimes (including x64-under-Rosetta) keep
BrowserStackLocal-darwin-x64, preserving current behavior.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: vivianludrick

lib/browserstack/localbinary.rb

@@ -55,7 +55,11 @@ def compute_binary_filename
     when /mswin|msys|mingw|cygwin|bccwin|wince|emc/
       'BrowserStackLocal.exe'
     when /darwin|mac os/
-      'BrowserStackLocal-darwin-x64'
+      if host_cpu =~ /arm64|aarch64/
+        'BrowserStackLocal-darwin-arm64'
+      else
+        'BrowserStackLocal-darwin-x64'
+      end
     when /linux/
       if host_cpu =~ /arm64|aarch64/
         'BrowserStackLocal-linux-arm64'

test/browserstack-local-test.rb

@@ -141,9 +141,16 @@ def test_alpine_x64_picks_alpine_binary
     end
   end
 
-  def test_darwin_arm64_picks_darwin_x64
-    # No darwin-arm64 binary; runs under Rosetta. Matches Node.
+  def test_darwin_arm64_picks_darwin_arm64
     with_host_config('darwin22', 'arm64') do
+      assert_equal 'BrowserStackLocal-darwin-arm64',
+                   BrowserStack::LocalBinary.new.send(:compute_binary_filename)
+    end
+  end
+
+  def test_darwin_x64_picks_darwin_x64
+    # x64 runtime (including x64-under-Rosetta) keeps the x64 binary
+    with_host_config('darwin22', 'x86_64') do
       assert_equal 'BrowserStackLocal-darwin-x64',
                    BrowserStack::LocalBinary.new.send(:compute_binary_filename)
     end