fix: lower priority fee and correct PlonkVerifier in deployer.rs

[alxiong]

Closes #2147

This PR:

• Switch to the right version of PlonkVerifier (in the deployer.rs we incorrectly deployed PlonkVerifier2.sol which is secure but less efficient)
• Use lower priority fee based on live gas oracle when sending out light client update transaction

Comments

• there is no dedicated price oracle for testnet (e.g. sepolia.etherscan.io), to avoid complicated logic, we simply keep using the same mainnet stats-informed gas pricing.