Replace .map instances with for loops in Repository class (abstractRepository.ts)

[3xtr4t3rr3str14l]

When I use the following benchmark to compare for loops and maps:

import {BenchmarkRunner} from "@chainsafe/lodestar-utils/test_utils/benchmark";

describe.only("", () => {
  it("", async () => {
    const runner = new BenchmarkRunner("produce block", {
      minMs: 1000,
      runs: 1024,
    });
    
    const length = 100000;
    const data = Array.from({length})
    await runner.run({
      id: "for loop",
      run: async () => {
        const values = [];
        for (let i = 0; i < length; i++) {
          values.push(data[i])
        }
      },
    });
    await runner.run({
      id: "map",
      run: async () => {
        data.map(i => i)
      },
    });
  })
})

I get the following results:

for loop    527.2788 ops/s      1.896530 ms/op   1025 runs    1.950 s
map         320.8606 ops/s      3.116618 ms/op    640 runs    2.001 s

We are currently using .map in keys(), values(), entries(). Maybe we can optimize by replacing the .maps with for loops.

[dapplion]

The time difference is only relevant when looping over large arrays. If the length i less than 1000 it really doesn't matter unless it's a super hot path. Try to analyze how frequently something is looped, if it's a hot path then we should 100% switch to raw for loops

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[dapplion]

Most hot paths looping over the entire validator set have been covered with #3760