feat: add custom EVM network support for local Anvil testnets

[mickvandijke]

Summary

Introduces --evm-rpc-url, --evm-payment-token, and --evm-payment-vault CLI flags (mirrored by ANT_EVM_RPC_URL / ANT_EVM_PAYMENT_TOKEN / ANT_EVM_PAYMENT_VAULT env vars) that override --evm-network, allowing nodes to point at a private Anvil instance with operator-deployed contracts instead of the public Arbitrum networks.

Adds a Custom { rpc_url, payment_token_address, payment_vault_address } variant to EvmNetworkConfig and threads it through NodeBuilder and WalletConfig via EvmNetwork::new_custom(...).

This is the same change already on mick/always-masque-relay (commit 8c3f0f3) — landing it on main avoids merge conflicts when that branch is rebased.

Motivation

The deploy/testnet-v2/ flow (and the external ant-testnet repo's testnet.py deploy) stands up a local Anvil droplet with the ANT token + payment vault deployed, then points every node at it. Without these flags, ant-node can only talk to Arbitrum One / Sepolia, so the testnet deploy fails with clap exit code 2 on unknown arguments.

Behaviour

• --evm-rpc-url set + both address flags set → uses EvmNetworkConfig::Custom (overrides --evm-network).
• --evm-rpc-url set but one of the address flags missing → hard error at startup.
• Neither set → unchanged behaviour (--evm-network preset applies).

Test plan

• cargo fmt --check passes
• cargo clippy --all-targets -- -D warnings passes
• cargo check --all-targets passes
• Manual: deploy local Anvil testnet and confirm nodes connect and accept payments against the custom contracts

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds support for pointing ant-node at a private/local EVM (e.g., Anvil) by allowing RPC URL + operator-deployed contract addresses to override the preset Arbitrum networks.

Changes:

• Introduces EvmNetworkConfig::Custom { rpc_url, payment_token_address, payment_vault_address }.
• Adds --evm-rpc-url, --evm-payment-token, --evm-payment-vault CLI flags (and env vars) to select the custom network and override --evm-network.
• Threads the new config through payment verifier network selection and wallet config construction.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 5 comments.

File	Description
src/config.rs	Adds Custom EVM network config variant and updates serde representation.
src/bin/ant-node/cli.rs	Adds CLI/env overrides to construct EvmNetworkConfig::Custom when --evm-rpc-url is set.
src/node.rs	Extends verifier setup to support EvmNetworkConfig::Custom.
src/payment/wallet.rs	Extends wallet config network mapping for Custom and adjusts constructor signature/tests.

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