feat(sdk-core): Add MegaETH support

[conwayconstar]

This pull request adds support for the MegaETH chain to the SDK by introducing its chain ID, addresses, and updating relevant address maps and tests. The main changes are grouped below by theme.

MegaETH Chain Support:

• Added ChainId.MEGAETH (4326) to the ChainId enum and included it in the SUPPORTED_CHAINS array, enabling MegaETH as a supported chain. [1] [2]
• Defined MEGAETH_ADDRESSES with all relevant contract addresses (e.g., factory, router, quoter, position manager) and added it to CHAIN_TO_ADDRESSES_MAP for chain-specific address resolution. [1] [2]

Address Maps Update:

• Added MegaETH-specific entries to V2_FACTORY_ADDRESSES and V2_ROUTER_ADDRESSES for correct contract address mapping. [1] [2]

Testing:

• Added a unit test to verify that SWAP_ROUTER_02_ADDRESSES returns the correct address for MegaETH, ensuring coverage for the new chain.