Check MacOS arch so the arm64 package would not be used for x86-64

[siphonelee]

My MacOS is x86-64, and when I tried to run "avalanche network start", I got an error like this:

avalanchego-v1.13.0 installation successful
AvalancheGo path: /Users/calvin/.avalanche-cli/bin/avalanchego/avalanchego-v1.13.0/avalanchego
Booting Network. Wait until healthy...
Error: fork/exec /Users/calvin/.avalanche-cli/bin/avalanchego/avalanchego-v1.13.0/avalanchego: bad CPU type in executable

Then I found out that avalanche didn't provide pre-built package for MacOS x86-64 (only for MacOS arm64), but in source code it checked OS type only without checking for arch type.

This is the fix and accordingly added/fixed test cases.

[felipemadero]

Thank you for the contribution and the detailed bug report! We've included your fix in #2994 with minor style adjustments to the error message.
We couldn't merge your PR directly due to branch protection requiring GPG-signed commits, so we applied the changes on our end.
Appreciate your thorough work including tests!