feat: add MegaETH Mainnet and fix Testnet chain ID

[kiyoakii]

Summary

• Add MegaETH Mainnet chain definition (chain ID: 4326)
• Fix MegaETH Testnet chain ID: 6342 → 6343

Details

Mainnet

Field	Value
Chain ID	4326
RPC	https://mainnet.megaeth.com/rpc
WebSocket	wss://mainnet.megaeth.com/ws
Multicall3	0xcA11bde05977b3631167028862bE2a173976CA11

Testnet Chain ID Fix

The current testnet definition has incorrect chain ID (6342). The actual chain ID is 6343.

Verification:

curl -s https://carrot.megaeth.com/rpc -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}'
# Returns: {"jsonrpc":"2.0","id":1,"result":"0x18c7"}  (6343)

References

• Mainnet on ethereum-lists/chains: https://github.com/ethereum-lists/chains/blob/master/_data/chains/eip155-4326.json
• Testnet on ethereum-lists/chains: https://github.com/ethereum-lists/chains/blob/master/_data/chains/eip155-6342.json (note: chain ID needs update there too)

[changeset-bot]

🦋 Changeset detected

Latest commit: 3eacaee

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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viem	Patch

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[sakulstra]

would you mind also adding the explorers section?
I think https://megaeth.blockscout.com/ is the one.

[yilongli]

Hi @sakulstra we don't have a canonical explorer at this point and we don't want to imply that the blockscout explorer is the default one. Is it OK to omit this section for now? We can submit a new PR if the situation changes.

[sakulstra]

I'm not a maintainer on that repo, but personally i think better to link "some" explorer than none.
A lot of ppl (including us) use the explorer configured here to render txn links etc. changing it down the line is no problem, but having non is pain.