infra(l1): move BenzoNet off a single validator to a multi-validator PoA set

[akash-mondal]

Tracker: #154

Context

BenzoNet (Subnet-EVM L1, chain id 68420) is currently a single-validator PoA testnet chain (README.md "What is Real vs. Simulated" + "Deployed on BenzoNet L1"). A single validator is a single point of failure — the chain already suffered a ~43h block-production halt (#145). A production institutional L1 needs a resilient validator set.

Scope

• Design the target validator topology (validator count, PoA validator-manager membership, host/geo spread). The Builder Console path is recommended (avalanche-cli is in maintenance mode).
• Plan validator onboarding via the validator manager, uptime expectations, and the dedicated-RPC-node separation (cf. Stand up the VM node topology: validator + dedicated RPC node via Docker Compose #25 topology).
• While re-standing nodes, source-verify BenzoNet contracts on the Blockscout explorer — the benzonet.json manifest currently has verified: false for all contracts.

Acceptance criteria

• A documented multi-validator topology + validator-manager membership plan.
• A migration/runbook from the single-validator chain (or a clean re-stand) that preserves the deployed eERC stack.
• BenzoNet contracts source-verified on explorer.benzo.space.

Dependencies

• Relates to closed infra issues Deploy BenzoNet PoA L1 to Fuji and initialize the validator manager #24 (validator manager), Stand up the VM node topology: validator + dedicated RPC node via Docker Compose #25 (node topology), Add monitoring, health checks, and P-Chain fee-balance alerting for BenzoNet #28 (monitoring), and the chore(infra): BenzoNet L1 halted — no blocks for ~43h, restart avalanchego block production #145 halt incident.
• BenzoNet stays testnet-only per go/no-go (no mainnet BenzoNet); this hardens the demo/institutional L1.