Make subnet contract creation less error-prone

Instead of each subnet operator creating their own completely independent subnets contract on the L1, we can instead have a single `hyperchains.clar` (deployed by Hiro) that implements core functionality, such as deposits and withdrawals. Individual subnets contracts could implement a trait, and call into the `hyperchains.clar` core contract.

This approach offers multiple benefits:
- Easier API integration for subnets events (can listen to hyperchains.clar)
- Easier version control / vulnerability patches (can create hyperchains-v2.clar simply)
- Makes subnets creation more accessible to a wider swath of developers
- Less involved auditing would be necessary for individual subnets

This change requires changes to hyperchains.clar, which currently manages only a single subnet.