Bug: Missing Apple Silicon (arm64) support for macOS

The current code hardcodes macOS to x64, which is incorrect for Apple Silicon (M1/M2/M3) Macs.

Current code:
/**
* All recent versions of Mac OS are 64-bit.
*/
if (process.platform === 'darwin') {
return 'x64'
}

Expected behavior:
- Return 'arm64' when running on Apple Silicon Mac (process.arch === 'arm64')
- Return 'x64' for Intel Macs

This package is widely used but hasn't been updated for Apple Silicon, causing wrong architecture detection on modern Macs.