feat: Using neverthrow to explicitly handle errors in AuthController

[karrui]

Problem

This is an extension PR for #215 to implement explicit error handling to the endpoints.

Solution

Improvements:

• Add explicit handling using neverthrow's FP-like Result class to return either success oks or error tracks for entire Auth module endpoints

Note that mail related files should technically be updated to be in their own module, and the other mail-related functions should also be converted to use Result. However, that is outside the scope of this PR and should be done in their respective PRs.

Tests

• Tests are refactored to use new FPfied methods for AuthService and MailService

New dependencies:

• neverthrow^2.7.1 - used to implement FP-like error handling

[karrui]

I'm so happy this passes now

[mantariksh]

nicely done! thank you for all the prior research and experimentation as well!