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

browserstack/local_binary.py

@@ -21,7 +21,10 @@ def __init__(self, key, error_object=None):
     source_url = self.fetch_source_url() + '/'
 
     if osname == 'Darwin':
-      self.http_path = source_url + "BrowserStackLocal-darwin-x64"
+      if platform.machine() in ('arm64', 'aarch64'):
+        self.http_path = source_url + "BrowserStackLocal-darwin-arm64"
+      else:
+        self.http_path = source_url + "BrowserStackLocal-darwin-x64"
     elif osname == 'Linux':
       if self.is_alpine():
         self.http_path = source_url + "BrowserStackLocal-alpine"