Leading Zeros Are Removed After dtypes Set to "string"

[chunkangwong]

Describe the bug
When using readCSV and readExcel, with a CSV file that contains zero-leading numbers, the leading zeros are not preserved even after setting dtypes to string

To Reproduce
Steps to reproduce the behavior:

1. Prepare the following .csv file:

./sample.csv

codes
012345
067890

import { readCSV, toJSON } from "danfojs";

const df = await readCSV("./sample.csv", { 
    frameConfig: {
        dtypes: ["string"],
    },
});
const data = toJSON(df);
console.log(data) // [{ codes: 12345 }, { codes: 67890 }]

Expected behavior
Leading-zeros should be retained if dtypes is string

Desktop (please complete the following information):

• OS: Windos 10
• Browser Chrome
• Version 1.1.1