fix(sdk): auto-detect platform in getBundleDownload

[DesmondDTD]

Summary

• Updated getBundleDownload() to automatically detect the current platform when one is not provided by the caller. This - ensures the request includes the required os and arch parameters for platform-specific bundles.

Changes

• Added automatic platform detection using MpakClient.detectPlatform() when no platform is supplied.
• Updated getBundleDownload() to include the detected os and arch values in the download request.
• Added a unit test verifying that platform detection occurs automatically when the platform parameter is omitted.

[mgoldsborough]

Thanks for the PR! We'll take a look.

In the meantime, would you mind dropping us a star on mpak and on https://github.com/NimbleBrainInc/nimblebrain?