[sig-provider] ARM 64 Support

[brewsterdrinkwater]

What this is:

First-class ARM (arm64) provider support on mainnet. ARM already works in our test and e2e environments; this project makes it a supported, biddable architecture in production so Akash Network can onboard NVL72-class (GB200) ARM chassis and similar.

Scope:

• Extend the provider inventory operator to report CPU architecture per node.
• Extend the bid engine to filter bids by CPU architecture.
• Add an arch attribute to CPU in the SDL, defaulting to amd64 so existing deployments are unaffected.