fix: update Xone Mainnet explorer URL to xonescan.com

[ruhil6789]

Description

This PR updates the block explorer URL for Xone Mainnet (Chain ID: 3721) to ensure MetaMask resolves the correct explorer when users view transactions or addresses.

The previous URL https://xscscan.com has been replaced with the correct explorer:
https://xonescan.com

This aligns the chain metadata with the official Xone Mainnet block explorer.

Changes

Updated explorer URL in _data/chains/eip155-3721.json
Old: https://xscscan.com
New: https://xonescan.com
No other fields were modified

Verification

All validations were completed successfully:
-> Ran schema + chain validation: ./gradlew run
->JSON formatting confirmed with Prettier (npx prettier)
-> File matches the chains metadata schema
-> Verified that https://xonescan.com/
is online and accessible

Related Issue

Fixes the incorrect explorer reference for Xone Mainnet as discussed here:
MetaMask/metamask-extension#30425 (comment)

[github-actions]

You successfully submitted a PR! Due to the amount of PRs coming in: we will only look at PRs that the CI is happy with. We can also not hold your hand getting the CI green - just look how others that where merged did it and RTFM. So as long as there is any CI check that reports an error - no human will look at this. You might be able to ask for some support after supporting the project - e.g. by sending funds to lists.eth. When you fixed things after a requested change - then you also need to (re-)request a review.