support multiple architectures for runtimes

[MattKiazyk]

Starting in Xcode 26 beta 2, Apple is now returning different runtime builds for different architectures.

Before

xcodes runtimes --include-betas

iOS 18.5 (Installed)
iOS 26.0-beta1 (Installed)
iOS 26.0-beta1 (Installed)
iOS 26.0-beta2
iOS 26.0-beta3
iOS 26.0
iOS 26.0

After

xcodes runtimes --include-betas

iOS 18.5  (Installed)
iOS 26.0-beta1 arm64|x86_64 (Installed)
iOS 26.0-beta1 arm64|x86_64 (Installed)
iOS 26.0-beta2 arm64|x86_64
iOS 26.0-beta2 arm64
iOS 26.0-beta3 arm64|x86_64
iOS 26.0-beta3 arm64

to fully install now, users will have to use iOS 26.0-beta3 arm64|x86_64 as the full identifier to distinguish the id as both have the same build version.

Installing via build version will still work but (I believe) will grab the universal variant.

NOTE: In this PR xcodes runtimes install "iOS 26.0-beta3 arm64" won't actually install the Apple Silicon variant. Need to add in support for -architectureVariant <universal|arm64> for the xcodebuild on Xcode 26 beta - logged in #436

[icedice]

Who should review and merge this?

edit:

I thought this would solve beta5 not showing up but that does not seem to be the case. I tried building the branch but beta5 still does not show.

[trentguillory-gc]

Nice update. And important improvement. I don't have any sway here, but I approve of these changes.

And #440 should be merged too.

[gianpispi]

I have no saying in this, but It looks good to me. Hopefully helping this to be merged since we can't use it right now.

[trsneed]

I would really like this merged too!