feat: file/range checksum support

[kukhariev]

Added option checksum to enable sha1/md5 rolling hashes.

import { uploadx } from '@uploadx/core';
import * as express from 'express';

const app = express();
app.all(
  '/files',
  uploadx({
    directory: 'upload',
    checksum: 'sha1',
    onComplete: file => {
      console.log('File upload complete: %s, sha1: %s', file.originalName, file.sha1);
      return file;
    }
  })
);

app.listen(3002);

The checksum of the uploaded data is updated every chunk and sent to the client via the x-range-sha1 or x-range-md5 headers:

HTTP/1.1 308 Resume Incomplete

X-Range-SHA1: a8b78179bd6bd0132acc9c9bf14739f3f42d2839
Range: bytes=0-3145727