lotus-gateway: Fix Filecoin.EthGetBalance

[coderabbitai]

Problem

The Filecoin.EthGetBalance RPC method is broken when accessed through lotus-gateway.

Task

Investigate and fix the Filecoin.EthGetBalance method to work correctly with lotus-gateway.

Context

• Parent issue: lotus-gateway: Fix broken RPC methods #6575
• Identified in: test: add lotus-gateway parity test #6570
• Requested by: @hanabi1224 at test: add lotus-gateway parity test #6570 (comment)
• Filter list: scripts/tests/api_compare/filter-list-gateway

[hanabi1224]

Bad request:

{
    "jsonrpc": "2.0",
    "method": "Filecoin.EthGetBalance",
    "params": [
      "0xff000000000000000000000000000000000003ec",
      {
        "blockHash": "0x11dde53937f937aada25c8a2aea7ca0819a70bc503f30355a2e26f3ee6cb1e5c",
        "requireCanonical": false
      }
    ],
    "id": 123
}

requireCanonical field is omitted by lotus-gateway and Forest failed to deserialize without it