fix: migrate example extension to hardhat v3

[rin-st]

Migrates the example extension's hardhat side to be compatible with hardhat v3 + rocketh (the base templates were migrated in create-eth, see PR #433). Without this, yarn cli ... -e scaffold-eth/create-eth-extensions:example fails after the backmerge.

What

File	Change
hardhat.config.ts.args.mjs	customNetwork → add type: "http" (hh-v3 requires a network type); drop invalid per-network verify block → declare custom block explorer via top-level chainDescriptors (keyed by chainId) + customNetwork.chainId; register the extension task via tasks: [...deployTasks, sayHelloTask]
deploy/01_deploy_se2_token.ts	old hardhat-deploy API (hre.getNamedAccounts()) → rocketh deployScript
tasks/index.ts	hh-v2 task().setAction(fn) → setInlineAction(...).build(), exported & registered in config
test/SE2Token.ts	hh-v2 import { ethers } from "hardhat" + typechain → typed Abi_SE2Token fixture (network.create() + loadAndExecuteDeploymentsFromFiles + getContractAt), mirroring the base test

(The next16 wagmiConfig lint fix is already on example via #122.)

Local validation (generated hardhat + extension instance, node 22.18)

• yarn compile ✓ (solc 0.8.20)
• yarn deploy ✓ (SE2Token deployed, deployedContracts.ts regenerated)
• yarn test ✓ (3 passing)
• hardhat:check-types ✓ (was 10 errors)
• hardhat:lint --max-warnings=0 ✓ / next:lint --max-warnings=0 ✓ / next:check-types ✓
• hardhat sayHello task ✓ (prints "Hello, World!", listed in --help)

Notes

• customNetwork.chainId: 99999 is a placeholder; the chainDescriptors custom-explorer flow was verified against installed hh-v3 type defs, not exercised against a real explorer.

🤖 Generated with Claude Code

[technophile-04]

Thanks @rin-st!