To install into Google Sheets, follow the "Creating a custom function" instructions found here: https://developers.google.com/apps-script/guides/sheets/functions and paste the snippet below into the editor. Follow the instructions to create a personal access token. After you install, use =TOTAL_CONTRIBUTIONS("yefim") in your sheet.

Code.js

/**
 *
 * YOUR GITHUB PERSONAL ACCESS TOKEN GOES BELOW!
 *
 * To create a token, follow these instructions: https://help.github.com/en/github/authenticating-to-github/creating-a-personal-access-token-for-the-command-line
 * For Step 7, only select the "read:user" scope.
 */
var PERSONAL_ACCESS_TOKEN = 'yourtokengoeshere';

var getDateRange = function(days) {
  days = days || 30;
  
  var today = new Date();
  today.setHours(0, 0, 0);
  today.setMilliseconds(0);
  
  var thirtyDaysAgo = new Date(today.valueOf());
  thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - days);
  
  return {from: thirtyDaysAgo, to: today};
}

var getRequestOptions = function(username, range) {
  username = username.substring(username.lastIndexOf('/') + 1); // strip everything after last slash

  var query = ['query {',
  'user(login: "' + username + '") {',
    'contributionsCollection(from: "' + range.from.toISOString() + '", to: "' + range.to.toISOString() + '") {',
      'startedAt',
      'endedAt',
      'contributionCalendar {',
        'totalContributions',
        'weeks {',
          'contributionDays {',
            'contributionCount',
            'date',
          '}',
        '}',
      '}',
    '}',
  '}',
'}'].join('\n');
  var options = {
    'method' : 'post',
    'contentType': 'application/json',
    'headers': {
      'Authorization': 'Bearer ' + PERSONAL_ACCESS_TOKEN
    },
    'payload' : JSON.stringify({query: query})
  };
  
  return options;
  
}

function TOTAL_DAYS_CONTRIBUTED(username, days) {
  if (PERSONAL_ACCESS_TOKEN === 'yourtokengoeshere') return 'Please fill in your personal access token by following the instructions inside the script.';
  if (!username) return 'Please pass a GitHub username or link as the first argument.';
  
  var range = getDateRange(days);
  var requestOptions = getRequestOptions(username, range);
  var textResponse = UrlFetchApp.fetch('https://api.github.com/graphql', requestOptions).getContentText();
  var res = JSON.parse(textResponse);
  
  var weeks = res.data.user.contributionsCollection.contributionCalendar.weeks;
  var totalDays = 0;
  
  // Count the contribution days
  weeks.forEach(function(week) {
    week.contributionDays.forEach(function(day) {
      if (day.contributionCount > 0) {
        totalDays += 1;
      }
    });
  });
  
  Logger.log(totalDays);
  return totalDays;
}

function TOTAL_CONTRIBUTIONS(username, days) {
  if (PERSONAL_ACCESS_TOKEN === 'yourtokengoeshere') return 'Please fill in your personal access token by following the instructions inside the script.';
  if (!username) return 'Please pass a GitHub username or link as the first argument.';
  
  var range = getDateRange(days);
  var requestOptions = getRequestOptions(username, range);
  var textResponse = UrlFetchApp.fetch('https://api.github.com/graphql', requestOptions).getContentText();
  var res = JSON.parse(textResponse);
  
  var contribs = res.data.user.contributionsCollection.contributionCalendar.totalContributions;
  Logger.log(contribs);
  return contribs;
}

Some example output

Video demo

https://streamable.com/j9abz

you da man