ref: convert mail and sms services into neverthrown variants

[karrui]

Problem

This PR improves the type safety and error handling of MailService and SmsService by refactoring the exposed functions into their neverthrown variants.

Sorry for the huge PR, they were pretty interconnected; I tried to make the commits as concise as possible for ease of reviewing commit-by-commit.

Closes #1260

Solution

Improvements:

• convert MailService functions to neverthrown variant
• convert SmsService functions to neverthrown variant
• use new neverthrown fns from mail and sms services in VerificationService
• store original thrown Twilio send errors in SmsSendError for logging purposes
• store original thrown mail send errors in MailSendError for logging purposes

Tests

• All affected tests have been updated to conform to the new refactored functions.

For mail service

• Create an email form, and add an email field with email verification and confirmation.
  1. Enter your email into the email form and verify your email. The email should be sent to the given email and the OTP should validate successfully.
  2. Submit the form. You (as form admin) should receive the usual form submission email with the correct answers. You (as the form filler) should also receive an acknowledgement email.

For sms service

• Create verified sms field. Go to form and check if sms is received
  • Give invalid OTP. Correct invalid otp error should be shown.
  • Turn off data in Chrome console and submit OTP. Correct unknown error should be shown.
  • Enter correct OTP. Should be verified correctly.
• Update emergency contact number
  • Give invalid OTP. Correct invalid otp error should be shown.
  • Turn off data in Chrome console and submit OTP. Correct unknown error should be shown.
  • Enter correct OTP. Should be verified correctly.

[mantariksh]

this is the way