Update Altcoinchain (chainId 2330) RPCs

[nucash-mining]

Both RPCs currently listed for Altcoinchain (chainId 2330) are dead:

• http://138.197.152.181:8145 — connection refused
• https://rpc0.altcoinchain.org/rpc — domain no longer resolves

This PR replaces them with the current public endpoint:

• https://rpc.wattxchange.app

Verification:

$ curl -s -X POST https://rpc.wattxchange.app -H 'content-type: application/json' \
    --data '{"jsonrpc":"2.0","id":1,"method":"eth_chainId","params":[]}'
{"jsonrpc":"2.0","id":1,"result":"0x91a"}   # 0x91a = 2330

The endpoint is synced and serving live blocks (height ~6,945,000 at time of writing).