fix: fixed chunkIntoN to chunk correctly

[rdvorkin]

chunkIntoN was chunking into N chunks, however it is used to chunk eth_getCode and eth_getProof responses into chunks of 2, so the desired action should be to chunk into chunks of length N https://github.com/ChainSafe/lodestar/blob/unstable/packages/prover/src/utils/evm.ts#L105

Because the current tests work on chunking array of length 4 into 2 the previous behavior was working and passing tests. When there are 6 requests the current behavior no longer works

[CLAassistant]

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[nflaig]

I'd would suggest to add more test cases for this to ensure it works with different values of arr and n, I have not worked with this part of the code base so you likely know better what value combinations are relevant. Alternatively, if it is just used with a value n=2, it might make sense to simplify the function.

import {expect} from "chai";
import {chunkIntoN} from "../../../src/utils/conversion.js";

describe("utils/conversion", () => {
  describe("chunkIntoN", () => {
    const testCases: {arr: number[]; n: number; expected: number[][]}[] = [
      {
        arr: [1, 2, 3, 4, 5, 6],
        n: 2,
        expected: [
          [1, 2],
          [3, 4],
          [5, 6],
        ],
      },
    ];

    for (const {arr, n, expected} of testCases) {
      it(`should convert ${JSON.stringify(arr)} into chunks of ${n} as ${JSON.stringify(expected)}`, () => {
        expect(chunkIntoN(arr, n)).to.be.deep.eq(expected);
      });
    }
  });
});

@nazarhussain can provide better feedback on this

[nazarhussain]

@rdvorkin That's seems a nice catch. Thanks for the PR.

Just add more tests cases as suggested by @nflaig and PR would be great. Also core more even n, odd n and lower than n cases.