Handle the case where the user's email requires verification

[robberwick]

This pull request adds support for the login response which indicates that the user's email address requires verification. It introduces a new base exception class PyLibreLinkUpError and refactors existing exceptions to inherit from it. Additionally, a new exception EmailVerificationError is added to handle email verification errors. Corresponding changes are made to the authentication logic and tests to accommodate this new exception.

Refactoring and New Exception:

• Introduced PyLibreLinkUpError as a base class for all custom exceptions in the pylibrelinkup module. (src/pylibrelinkup/exceptions.py)
• Added a new exception EmailVerificationError to handle scenarios where the user needs to verify their email. (src/pylibrelinkup/exceptions.py)

Authentication Logic Update:

• Updated the authenticate method to raise EmailVerificationError when the authentication response indicates that email verification is required. (src/pylibrelinkup/pylibrelinkup.py)

Test Enhancements:

• Added a new test fixture email_verification_response_json to provide mock data for email verification responses. (tests/conftest.py)
• Created a new test case to ensure the authenticate method raises EmailVerificationError when appropriate. (tests/test_client_authentication.py)
• Added a new JSON file email_verification_response.json containing mock data for email verification responses. (tests/data/email_verification_response.json)