feat(cli): add --verify-contract flag to rex deploy

[ilitteri]

Motivation

After deploying a contract with rex deploy --contract-path, there's no way to verify the source code on Etherscan. Users have to manually submit verification through the Etherscan web UI or a separate tool. This adds a one-command deploy+verify workflow.

Description

Adds --verify-contract flag to rex deploy that automatically verifies the contract source code on Etherscan after deployment using the Etherscan V2 API.

New CLI flags:

Flag	Description
--verify-contract	Enable post-deploy Etherscan verification
--etherscan-api-key	API key (also reads ETHERSCAN_API_KEY env var)
--contract-name	Override contract name for multi-contract files
--optimizations	Number of optimizer runs for solc and Etherscan

How it works:

1. Deploys the contract and waits for the receipt
2. Builds a Standard JSON Input matching the exact solc flags used during compilation (--via-ir, --no-cbor-metadata, optimizer settings)
3. Recursively resolves imports to populate the sources map
4. Submits verification to Etherscan V2 API (retries if Etherscan hasn't indexed the contract yet)
5. Polls verification status until success

Changes:

• cli/src/verify.rs — new module with all verification logic
• cli/src/common.rs — new flags on DeployArgs
• cli/src/cli.rs — refactored compile_contract_from_path to return CompilationInfo (bytecode + remappings + optimizer settings), deferred artifact cleanup, wired verification after deploy
• cli/Cargo.toml — added reqwest and regex dependencies
• cli/README.md — documented the new flags with examples

Tested on Sepolia:

$ rex deploy --contract-path Counter.sol --remappings "" --optimizations 999999 \
    --verify-contract --etherscan-api-key $KEY --private-key $PK \
    --rpc-url https://ethereum-sepolia-rpc.publicnode.com

Compiler run successful. Artifact(s) can be found in directory "./solc_out".
Contract deployed in tx: 0x7f35...
Contract address: 0x2246...

Verifying contract on Etherscan...
  Compiler version: v0.8.31+commit.fd3a2265
  Contract name: Counter
  Submitting verification request...
  [1/12] Waiting for Etherscan to index the contract...
  [2/12] Waiting for Etherscan to index the contract...
  Verification submitted (GUID: vnr1ag...)
  [1/60] Checking verification status...
  Contract is already verified.
  https://sepolia.etherscan.io/address/0x2246...#code