Replace bundled AzCopy binaries with platform-specific install hook

[craxal]

The azcopy-node package and its platform-specific variants (azcopy-win32-x64, azcopy-darwin-arm64, etc.) bundle AzCopy binaries directly in the npm package. This is flagged as non-compliant under Foreign Checked-In Binaries (FCIB) policy.

Proposed solution

Add an install hook to azcopy-node that downloads the correct AzCopy binary for the target machine's platform and architecture at npm install time, rather than shipping pre-bundled binaries in separate packages.

Benefits

• Eliminates FCIB compliance issue — no checked-in binaries
• Removes the need for separate azcopy-{platform}-{arch} packages
• Simplifies the dependency graph

Considerations

• Install hook needs to work in CI environments (may need offline/cache support)
• Need a reliable download source for AzCopy binaries (official Microsoft CDN)
• Checksum verification of downloaded binaries
• Fallback behavior if download fails
• Air-gapped / restricted network environments