[docs] Document ERC-2470 and predictable EVM contract deployments on Nibiru

[Unique-Divine]

Context

Nibiru#2697 adds the canonical ERC-2470 Singleton Factory to Nibiru's default EVM genesis. We should document how developers can use ERC-2470 and CREATE2 for predictable EVM contract addresses on Nibiru.

Scope

• Explain the CREATE2 address formula and the inputs that must match:
  • factory/deployer address
  • salt
  • complete creation bytecode (initCode), including constructor arguments
• Document the canonical ERC-2470 factory address and its deploy(bytes,bytes32) interface.
• Show how to predict an address before deployment and verify it through EVM JSON-RPC.
• Explain that Nibiru includes the factory in default EVM genesis for new chains and that the same pattern is conventional across many EVM networks.
• Include practical examples for Foundry/cast or equivalent tooling.
• Call out important caveats:
  • constructor msg.sender is the factory
  • constructor arguments affect the address
  • initialization should be atomic where possible
  • salts are namespaces, not secrets
  • CREATE2 does not itself guarantee identical runtime behavior if init code is chain-dependent
• Link to PR feat(evm): Add ERC-2470 Singleton Factory to Default EVM Genesis #2697 and the official ERC-2470 specification.

Acceptance Criteria

• Nibiru developer documentation has a dedicated ERC-2470/CREATE2 section.
• A reader can calculate a predicted address, deploy through the factory, and verify the result using documented commands.
• The docs distinguish deterministic address calculation from proxy upgradeability and from Wasm instantiate2.
• Examples work against Nibiru localnet and identify the mainnet/testnet RPC endpoints or endpoint configuration pattern.