Fix AxelarReporter unsupported-chain validation

[coderabbitai]

Summary

AxelarReporter._dispatch does not correctly reject an unsupported target chain when chainNames[targetChainId] has not been configured.

Required change

In veashi-contracts/src/adapters/axelar/AxelarReporter.sol, update the target-chain support check to detect the default empty string from the chainNames mapping using a raw empty-string check (for example, bytes(targetChainName).length == 0), while preserving the existing ChainIdNotSupported(targetChainId) revert.

Rationale

abi.encode(targetChainName) includes ABI offset and length metadata. Consequently, hashing abi.encode("") is different from keccak256(""), so the existing check does not recognize a missing mapping entry and can proceed with an empty Axelar destination chain name.

Affected area

• veashi-contracts/src/adapters/axelar/AxelarReporter.sol
• AxelarReporter._dispatch

Acceptance criteria

• An unconfigured chainNames[targetChainId] entry reverts with ChainIdNotSupported(targetChainId).
• Configured, non-empty Axelar chain names continue to dispatch normally.
• Tests cover both the unconfigured-chain revert and a configured-chain path.

Backlinks

• PR: Feat/axelar veashi #504
• Review comment: Feat/axelar veashi #504 (comment)
• Requested by: @mani99brar