Add mainnet REO contract address

[cargopete]

Summary

• Adds the Rewards Eligibility Oracle (REO) mainnet contract address to the issuance addresses registry
• Address: 0x8ec2767a9d9ba02b4e09e8ff4fac2e14a340f304
• Network: Arbitrum One (chainId: 42161)

Context

The REO dashboard dynamically fetches contract addresses from this registry. Adding the mainnet address enables the dashboard to display mainnet data.

[RembrandtK]

I have this on another branch. Do you need it on main for the dashboard to pick it up?

[cargopete]

I have this on another branch. Do you need it on main for the dashboard to pick it up?

Yes, the dashboard fetches addresses.json from main - it hits raw.githubusercontent.com/graphprotocol/contracts/refs/heads/main/packages/issuance/addresses.json directly. So the mainnet address needs to land on main for it to be picked up. If you already have it on another branch, happy to close this PR and just merge yours instead - whichever's easier.