SDK-5741: Migrate browserstack-sdk install from PyPI to S3

Update requirements.txt to install browserstack-sdk from BrowserStack-hosted
S3 instead of PyPI, as PyPI flagged the package for obfuscated code.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: agrawal-ayush

requirements.txt

@@ -1,3 +1,3 @@
 browserstack-local >= 1.2.3
 selenium
-browserstack-sdk
+browserstack-sdk @ https://sdk-assets.browserstack.com/python/browserstack_sdk-latest.tar.gz