Integrate the first on-the-fly (feature flag) migration with FVM

[fxamacker]

Updates onflow/cadence#3584

We need to integrate our first on-the-fly (feature flag and non-HCU) migration with FVM.

• OKR (Sep 2024): Combine non-atree domain payloads into atree payloads cadence#3584
• HCU (Oct 2024): Combine domain payloads and provide on-the-fly migration cadence#3664
• Feature Flag (Nov 2024): [Account Storage Maps] Refactor storage into V1 and V2 cadence#3678

Note

As the first feature flag migration, this work can help other projects requiring feature flag or on-the-fly migrations.

Additionally, full migration test using Nov 1 mainnet data showed:

• -440 million (-28.8%) reduction in payload count
• -180 million (also -28.8%) reduction in mtrie node count
• -11.4% reduction in state size

Considerations

Full benefits of migration will be realized after all accounts are migrated. Given this, we want to migrate more than the authorizing account. E.g. it seems possible to migrate accounts that got touched in a transaction.

In the Execution team sync (Nov 20), @janezpodhostnik took time to answer some questions from the team. We can:

• prevent migrations from affecting transaction fees
• enforce a limit on max number of migrated accounts per transaction
• prevent migration from failing the transaction (e.g. won't fail transaction if migrating causes storage capacity to be exceeded)

Additional considerations were also discussed during the Execution team sync.

NOTE: Migrating domain registers to atree will touch <= 20 registers for each account. Currently, we have 9 domains in Cadence and accounts average 4-5 domains on mainnet.